# Which is the correct equation?

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Introduction

Which Is the Correct Equation? Aim To design an experiment to measure a volume of gas that will show which of the two equations given is more likely to be the correct volume. Experiment Equations (s) Equation 1: 2 KNO3 (s) 2 KNO2 (s) + O2 (g) Equation 2: 2 KNO3 (s) K2O (s) + 2 NO2 (g) + 1/2 O2 (g) Risk assessment/ Safety. Safety while working in the chemistry lab is must if I want to achieve accurate and reliable results in conjunction with not harming my self or other chemists around me. Some of the precautions I will undertake: * Wearing safety goggles at all times, this ensures that no chemicals make contact with my eyes. * Wearing a laboratory coat to ensure that there are no spillages onto my clothing. * Using a bench mat to avoid spillages onto my work bench. * Nitrogen dioxide2 (gas) - Highly toxic by inhalation, can be fatal. Severe respiratory irritant. Gloves must be worn and syringes that contain the gas must be dismantled in the fume cupboard while wearing a face mask. * Potassium nitrate - inhalation causes irritation to the respiratory tract. ...read more.

Middle

This will ensure there is no need to transfer from potassium nitrate from different containers unnecessarily. * Replicating the experiment makes the results reproducible and highlight anomalies, therefore increasing the reliability of the experiment. * Calculations I have decided to aim for 80cm3 of gas to be produced. I have chosen this volume because it is a number that will give a more reliable result. Since the capacity of the syringe is 100cm3, anything less than 100cm3 would not give a reliable result. However, using the appropriate mass of potassium to produce a volume of gas more than 80/85cm3 would carry a risk of expanding to greater volume of the syringes capacity (due to heating). Furthermore, the balance has an error so there is again the chance of overfilling the syringe. The first thing that will need to be calculated is how many grams of potassium nitrate I will need. To find this I will use the equation: Moles = volume of gas � 24000 cm3 I will substitute this formula into equation 2 as it produces the most gas (this is because there is a risk of overfilling the syringe if I use equation 1, but the more accurate equation is 2): 2 KNO3 (s) K2O (s) ...read more.

Conclusion

Firstly I will need to convert the 0.27g of potassium nitrate into a molar value; Moles = 0.27g � (39.1 + 14 + (16 x 3)) = 0.27g � 101.1 = 2.67 x 10-3 Step 2 However the molar value calculated is for two moles (2:1 ratio of potassium nitrate to oxygen). Therefore, to convert it into a value of one mole, I will divide by two. 2.67 x 10-3 � 2 = 1.335 x 10-3 mol Step 3 Since I know the number of moles of the oxygen gas, I can substitute this value into the equation Mass (g) = Moles x 24000cm3. = (1.335 x 10-3) x 24000cm3 = 32.0cm3 Therefore, total % Error for equation 1 = % Error of syringe ((1�32.0) x 100) + % Error of 2dp balance (7.40) = 3.1 + 7.40 = 10.5% 10.5% of 32.0cm3 = 3.37 therefore, the ranges of values for equation 1 are: 30.3 --> 32.0 --> 33.7cm3 If the volume of gas produced lies somewhat between this range, then equation 1 is correct. So, I know that by considering apparatus error it can be possible to distinguish which equation is 'correct'. However, there may be others that are no quantifiable. For example, if 55cm3 was the result you would not be able to tell which equation was correct. ...read more.

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