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To determine the enthalpy changes of reaction for some reactive metals, with hydrochloric acid.

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Introduction

To determine the enthalpy changes of reaction for some reactive metals, with hydrochloric acid. Sodium carbonate can be used as a standard to determine acid concentration, because it is readily available in a pure and dry form. Here 7.5g is used to make up a 250cm solution with a concentration of 0.283 moldm .The calculations show this; The exact concentration of hydrocloric acid, is found by titrating it against the standard solution. Apparatus Chemicals 2 decimal place balance; HCl (exact weighing jar; concentration not known teat pipette; between 2.0 and 2.5moldm); pipette; burette; screened methyl orange; conical flask; anhydrous sodium carbonate. 250cm measuring flask and bung; 100cm measuring cylinder; white tile; clamp stand. Safety points. Solutions of HCl greater than or equal to 2moldm are irritant to the skin and eyes. A lab coat should be worn and direct contact with acid avoided. Na CO is also irritant, same preucautions should be taken. ...read more.

Middle

Repeat titration (using same standard) until 3 results within 0.1cm are obtained. Record all results but only use the values which are in agreement to calculate the mean volume used. Calculation of hydrocloric acid concentration. When chemical bonds are broken energy is required, when new bonds are formed, energy is given out. An exothermic reaction is a reaction which overall gives out more energy than it takes in. We can calculate this enthalpy change in a reaction by measuring the temperature change. The five metals in this method are potassium, magnesium, lithium, calcium and zinc. They are selected because they are all fairly reactive and are all safe to react with 2moldm of HCl. The come from a variety of groups from the periodic table. I am using 0.3g of each metal as in larger quantities the reaction could be dangerous, and the hydrogen released explosive. For a fair test all metals should react in the same quantaty of acid. ...read more.

Conclusion

Some of the products formed are corrosive and cause burns to the skin so contact must be avoided with all chemicals e.g. Aluminium chloride is corrosive. A lab coat should be worn at all times. Enthalpy change = mc t The HCl is made up mainly from water, so we can use water's data: The specific heat capacity C of water =4.2JK g , and the mass 1cm=1g. m = mass of HCl + mass of metal =50g +0.3g =50.3g T is the temperature change in K or C In my trial I obtained a T value of 17 C for magnesium Enthalpy change = 50.3 x 4.2 x 17 = -3890 J To convert to moles: moles of Mg = mass = 0.3 = 0.0125 RFM 2.4 0.0125moles of Mg give an enthalpy change of -3590 J so 1 mole of Mg gives - 287000 J mol = -287KJ mol To simplify for each metal, in this particular reaction only enthalpy change = mc t x mol/1000 = 50.3 x 4.2 x t x 80 /1000 =(16.9008 x t) KJmol ...read more.

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