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GCSE: Aqueous Chemistry
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The rates of aqueous reactions
- 1 The rate of reaction can be increased by increasing the concentration of the solution. This will mean there are more molecules in the same amount of space, so there will be more collisions.
- 2 The rate of reaction can be increased by increasing the temperature of the solution. This will give the molecules more energy, making them move faster and collide more. It will also mean they stand a better chance of having the activation energy.
- 3 The rate of reaction can be increased by increasing the pressure of the solution. This will mean there are more molecules in the same amount of space, so there will be more collisions.
- 4 Adding a catalyst to the solution will increase the rate of reaction. This is because the catalyst lowers the activation energy needed for the solution to react.
The definition for rate of reaction is “change in concentration of product or reactant over time”.
It has the units mol dm-3 s-1
How to calculate the number of moles in a solution
The two most important equations to learn are:
moles = mass / Mr and moles = volume x concentration
If you know the moles of one chemical in your balanced equation, you can find out the moles of anything else by looking at the “big number” ratios. For example:
2NaOH + H2SO4 = Na2SO4 + 2H2O
If you had 10 moles of H2SO4, because there is a 2:1 ratio, you would have 20 moles of NaOH.
- 3 Your volume MUST be converted into dm3 before you use it in your equation. To convert cm3 into dm3 divide your number by 1000.
- 4 Do not forget to round your answer to a sensible number of significant figures (usually the least amount of significant figures that the question itself goes to).
- 5 Your Mr can be found by looking at the mass number on the periodic table (this is the bigger of the two numbers- the smaller one is called the proton number
Top tips for aqueous reactions
- 1 Anything that is dissolved in an aqueous solution will have the state symbols (aq). For Na+(aq)
- 2 If your reaction is dissolved in water, then water will have the state symbol (l), for “liquid”.
- 3 If the question says that your reaction is done under standard conditions, then it means at 1 atmosphere of pressure, at 25'C.
- 4 When constructing balanced reactions, do not forget to balance your charges when making salts. For example: HCl + Mg = MgCl + 0.5H2 would be wrong. The correct answer would be 2HCl + Mg = MgCl2 + H2.
- 5 The most important equation reaction to remember is acid + base = salt + water. This crops up all of the time in exams!
This procedure can help you find the chemically equivalent volume of two solutions. It is done by slowly adding one solution with another until the reaction has been completed. The end point is usually indicated with an indicator solution that changes colour when the right amount of OH � ions have been added. I will be using a number of pieces of equipment, including a burette, pipette, conical flask, electronic balance, beaker, 0.1 mol/dm� sodium hydroxide, vinegar, deionised water and a selection of indicators which I have to make a decision on which to use.
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Determine the concentration or molarity of Ethanoic acid (CH3COOH) in two types of commercial vinegar.
be needed to neutralise the ethanoic acid in the vinegar of which two different kinds will be studied and from there calculations can be made to find out the concentration of the ethanoic acid which will be discussed later. The next step is to find out a suitable indicator for the titration. The type of indicator required in this case is one which changes colour very rapidly at the equivalence point and so gives an accurate idea as to when the ethanoic acid has been neutralised.
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This type of reaction involves the transfer of electrons from one unit to another. The oxidation number of all elements is always zero e.g. oxidation number of Fe in the metallic form is zero however the oxidation number of a substance as a monatomic ion equals the charge of that ion.1 Oxidation and Reduction can be defined by the following: Oxidation: the part in an oxidation-reduction reaction in which there is a loss of electrons by a species (or an increase in the oxidation number of an atom) 1 Reduction: the part in an oxidation-reduction reaction in which there is a gain of electrons by a species (or an decrease in the oxidation number of an atom)
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Explain how the enthalpy change of neutralisation can be used to determine the relative strength of an unknown acid.
CH3COOH (aq) H+ (aq) + CH3COO- (aq). For every 250 molecules of ethanoic acid, only 1 molecule dissociates and only a small proportion of the potential acidic power is released as H+. A weak acid only partially dissociates into ions. Strong Acids: When an acid dissolves in water, a proton (hydrogen ion) is transferred to a water molecule to produce a hydroxonium ion and a negative ion depending on what acid you are starting from. In the general case: These reactions are all reversible, but in some cases, the acid is so good at giving away hydrogen ions that we can think of the reaction as being one-way.
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(H2O) (CaCl2) Prediction I think that the stronger the acid the faster the rate of reaction will be. This is because the rate of reaction is decided upon how often and how hard the reacting particles collide with each other. So, if the acid is more concentrated then there are more particles to collide with the marble chips. However, the particles need enough energy to make a reaction. The minimum energy for a reaction to happen is called the activation energy. This makes the particles move quicker therefore will hit each other more often and with greater force.
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Shpw how different types of antacids neutralise acidic conditions and the speed in which they do it.
Antacids are not just use to neutralise acidic conditions in humans but in practically every aspect of life. They are use to neutralise acidic lakes so animal and plant life can prosper, neutralise soils for crops to grow even in the production of certain foods to increase the taste. The differences with acids and alkalines are acids have a lot of hydrogen ions this distinguishes them from alkalines which have a lot of hydroxide ions. It is this fact that can determine an acid from base and their p.h as it is reasonable to assume the higher the concentration of hydrogen or hydroxide ions in a solution then the more acidic or alkaline it is.
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get somewhere colder they then transfer their energy by their usual process of collisions, which warms up the surroundings. In order to stop convection in this experiment I will put a lid over the can to stop it. This is why I will use two different types of materials in each test, one of he materials will be the lid and the other will be the material which will be covered around the can to limit conduction and radiation. So as the particles rise the hotter particles will bounce off the lid and remain in the can to keep the water warm or at the optimum temperature 500c.
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I am going to use the enthalpy change -50.1, CH3COOH. The specific heat capacity is 4.18 Jg-1 K-1. Enthalpy Change = Mass x Specific Heat Capacity x Temperature Change ?H = -MC?T -50.1 = -M x 4.18 x 13 -50.1 = -M x 54.34 -50.1 = -M x 54.34 x 1 0.1 -50.1 = - M x 543.4 -50.1 = -M 543.4 -0.092197276 = -M M = 0.092 g I am going to use the NaOH as 0.1M because I want it to be the same concentration as the unknown acid as the unknown acid is monoprotic, where one mole of acid reacts with one mole of hydrogen.
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This is because the acid particles gain more energy and have a lot more successful collisions. A successful collision is when more hydrochloric acid particles collide with the limestone more often. Therefore I think that my prediction that as the temperature increases the limestone will react with the hydrochloric acid quicker will be true. This is because the temperature gives the hydrochloric acid particles more energy, so they move faster and collide with the calcium carbonate more often to break the bonds. The separated particles then join to form water, carbon dioxide and calcium chloride. Stephanie Fletcher Basic Method Thermometer Heating the hydrochloric acid to the correct temperature.
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HOOC(CH2)nCOOH H = 1 O = 16 C = 12 Mr when n = 1 1+16+16+12 (12+2) 12+16+16+1 = 104 Mr when n = 2 1+16+16+12 [(12+2) x2] 12+16+16+1 = 118 Mr when n = 3 1+16+16+12 [(12+2) x3] 12+16+16+1 = 132 Mr when n = 4 1+16+16+12 [(12+2) x4] 12+16+16+1 = 146 From these calculations I can see that I need between 104g and 146g in 1 litre to equal 1M. But I want the solution in 250cm3, so therefore I need to divide the weights by 4: n = 1 104 = 26g So I need between 26g and 36.5g in 250cm3 to make a 1M 4 solution.
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-Top up volumetric flask with distilled water carefully up to the 250cm3 line and then shake solution thoroughly. Titration -Collect apparatus as shown above. -Using the distilled water, rinse out all equipment, to rid any other substances. -Transfer 25cm3 of Sulphuric Acid with a pipette into a clean conical flask. -Pour 50cm3 of the Sodium Carbonate solution into the burette with a funnel and take out the funnel. -Add a few drops of methyl orange indicator solution to the Sulphuric Acid in the conical flask. -Record the reading on the burette before starting the titration. -Add small amounts of Sodium Carbonate solution from the burette into the conical flask, swirling the flask and rinsing the end of the burette after every addition.
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Determine the percent aspirin in an aspirin tablet and to compare this with the amount specified on the label.
* Calculate the percent purity of aspirin in one aspirin tablet to the specified amount on the label. Introduction A titration is the basis of titrimetiric analysis. It is in which a solution containing a known concentration of a reagent is added to a solution containing an unknown concentration of a substance (In this case the sodium hydroxide remaining after hydrolysing acetyl salicylic acid) until the reaction between the reagent and the substance is complete. The solution of known concentration is called a standard solution and is the titrant (In this case hydrochloric acid).
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The aim on my investigation is to find the percentage of citric acid present in lemon squash by using a method of neutralisation, by a method of titration and volumetric analysis.
The concentrated acid is a 35% by weight solution hydrogen chloride in water. It is a typical strong acid. It reacts with metals, alkalis and bases, carbonates and indicators in the same way that all strong acid do. Manufacture of hydrochloric acid Hydrogen chloride is made industrially by burning hydrogen in chlorine. It is also a valuable by- product of many processes in which chlorine is reacted with organic compounds. Uses of hydrochloric acid In the laboratory, concentrated hydrochloric acid will produce chlorine if added to potassium permanganate crystals. Hydrochloric acid + oxygen atoms from chlorine + water Potassium Permanganate 2HCl (aq)
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* Mass of chips - if two chips had the same surface area at the start of the experiment, but one had a higher mass than the other, it would take longer to dissolve and so during the experiment it would have a higher surface area, meaning more area to conduct reactions. This would mean that it would be an unfair experiment. * Amount of acid - during the experiment, if the reduction in the amount of acid in the conical flask means that all parts of all chips are not in contact with acid, it will also distort the results.
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To investigate three factors that affect the rate of cooling a liquid and to test these factors to see exactly how much they affect the rate of cooling water.
to its volume (V): * For a cube of side l o A1 / V1 = 6 ? l 2/ l3 = 6 / l * Finally, when there is a temperature difference between two bodies, energy is transferred from the hotter to the colder, until they reach the same temperature. This is known as the Zerath Law of Thermodynamics. Identifying the Variables The variables that affect the rate of cooling liquid that I am going to investigate in this coursework are: Insulation Insulators are bad conductors, so instead of taking in heat like conductors, they effectively act as a barrier to stop heating from passing through.
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These chemicals have been known to people interested in medicine for centuries. One of the first and most influential physicians, Hippocrates, wrote about a bitter powder extracted from willow bark that could ease aches and pains and reduce fevers as long ago as the fifth century B.C. In the 1700s, the scientist Reverend Edmund Stone wrote about the success of the bark and the willow in the cure of the "agues," or fevers with aches. With a bit of chemical detective work, scientists found out that the part of willow bark that was (1)
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or lethal concentration (LC), where death is the criterion of toxicity. Results are shown, for example, as LC50 that indicates 50% mortality of the organisms at a certain concentration. Time is also an important factor in these studies so it must be indicated in results (Mason 1991). Organisms such as Daphnia are often used in laboratory experiments to determine the LC50 of a substance. The damage done as the dose changes in a given time determines the results of the experiment. Most commonly, the threshold of 50% mortality, of varying concentrations in a specified time, is used and is known as the median lethal concentration (Jeffries & Mills, 1990).
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We also decided to use a 1-mole/dm3 concentration as we found 0.5 mole/dm3 was too little for a good result, and 2 moles/dm3 was too violent. The preliminary work also showed that it was necessary to use a good insulating material to house the reaction in and we also needed to use very accurate equipment. Safety As with any experiment there are safety issues that need to be followed. Many of the acids or alkalis used in this experiment are corrosives or irritants therefore safety goggles must be worn at all times.
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The solution in the conical flask will have a fixed volume to start with until the solution in the burette is added to it and a visible colour change has occurred which means the two solutions have reacted together. Often an indicator is added to show when the reaction is finished to show the end point of a titration between an acid and an alkali an indicator can normally be used. The indicator can show when the base has been neutralised completely.
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so as the penguin's huddle they radiate heat to other penguins to keep each other warm. Predictions I think that when penguins huddle. They do it to keep warm. So I my experiment the more test tube together in a huddle the warm the water will stay. I think this because of the radiation given off the test tubes. Also the cooler that water goes the slower the temperature will go down. As the water is going down to room temperature.
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So if a solution is more concentrated more particles are bumping into each other. Which makes more collisions so there are more reactions between particles, therefore more reactants that produce more water. When water is produced there bonds release energy therefore the more water produced by the reacting OH- and H+ ions the bigger the temperature rise. This is called collision theory examples of this are shown by the diagrams below. I will record the temperature change of each experiment to find out how concentration can affect the output variable. I will keep the concentration of the alkali constant and change the concentration of the acid.
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The dirt is then pulled off the object as it is rinsed again. But, when there are calcium or magnesium ions, then the calcium or magnesium reacts with the soap to form calcium stearate or magnesium stearate. This solid is scum. Ca2+(aq) + 2St-(aq) CaSt2(s) Calcium + Stearate Calcium Stearate (scum) Mg2+(aq) + 2St-(aq) MgSt2(s) Magnesium + Stearate Magnesium Stearate (scum) The chemical formula for soap is: Prediction For my preliminary experiment, I needed to find out which metal ions form a lather with soap solution and which metal ions form scum. Approximately 2cm3 of the metal ion was put into a test tube and approximately 2cm3 of soap solution was added.
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* Use a pipette filler to rinse the pipette with water and the sodium carbonate solution. 25.0 cm3 of sodium carbonate solution is then carefully transferred to a clean 250 cm3 conical flask. Note that this first flask is usually taken as a trial run as the end-point is probably overshot. * Run the diluted hydrochloric acid from the burette into the flask. The flask is swirled until the colour of solution has just changed from yellow to pale orange. The final burette reading was recorded. * Refill the burette with the acid, and take down the initial reading again.
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Investigating the hypothesis that the higher the increase in the concentration of Bile salts, the faster Lipase will hydrolyse fat.
To these test tubes, 5cm3 of milk was placed in each, using the 5cm3 graduated pipette. Careful consideration was given so that the liquid was measured from the bottom of the meniscus each time. This was to ensure that all measurements were accurate and also equal to all of the test tubes. This method was also followed when 7cm3 of sodium carbonate solution was further added to each of the test tubes using the 10cm3 graduated pipette. Into this mixture was added the following measurements of the bile salts: Into the first test tube - using a 1cm3 graduated pipette, 1cm3 of bile salts was added.
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To investigate the effect of changing the concentration of acid on the rate of reaction of Magnesium and Hydrochloric Acid.
This means that the overall volume of the liquid is the same all the time, but just varying concentrations. I have decided to do five variations. I think this will be the right amount to as it is enough to form a valid conclusion but not too much that I won't have time for repeats. In order to make sure that this is a fair test and the results are accurate, I will repeat the whole experiment twice and work out the average.
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