Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: jessica Gwin on May 18, 2006, 08:08:57 PM
-
Could someone help me with these questions. Thank you!!
1. When excess lumps of sodium hydrogen carbonate are added to dilute hydrochloric acid the following reaction takes place.
NaHCO3(s) + HCl(aq) ----> NaCl(aq) + CO2(g) + H2O(l)
Outline two ways in which the rate of this reaction could be studied. In each case sketch a graph to show how the value of the chosen variable would change with time.
2. State and explain whether the total volume of carbon dioxide gas produced would increase, decrease or stay the same if...
a) more lumps of sodium hydrogen carbonate were used
b) the experiments were carried out at a higher temperature
-
Can you show an attempt at the answer first?
-
is it a closed container?
-
The questions don't state whether its a closed container or not.
For the first question I put:
1. Weigh the reactants every 15 seconds to see how the mass decreases
I'm not sure about the 2nd way
For the second question I put:
a) Increase because the concentration increases
b) Increase because more molecules will have enough energy to react.
I'm not sure if these are right though.
-
1. Yes you could weigh the reactants in theory, although a bit hard in practice. I suppose you could weigh the entire reaction and over time the release of carbon dioxide could be recorded. Or what about directly measuring the amount of carbon dioxide given off? I am not sure about the details but you could possibly measure the pH of the solution over time and see how much the HCl decreases.
2.a) I agree the carbon dioxide would increase. So long as there was still HCl to react with it though. If HCl was the limiting reagent then this would not happen, but I think you assum HCl is in excess.
b) Well I would say that the "total volume of carbon dioxide produced" would stay the same. Because, increasing the temperature would in theory increase the rate at which the carbon dioxide was produced but in the end you still produce the same amount of CO2, just faster, if you get me. In other words a set amount of reactants will only produce a set amount of products, heating it will just for that amount of products quicker.
-
okay thanks :)
one more question:
if I was to sketch a graph for the amount of carbon dioxide given off would the graph increase or decrease?
-
if I was to sketch a graph for the amount of carbon dioxide given off would the graph increase or decrease?
Well this depends on what you are trying to show with your graph. Lets assume you want to show the amount of CO2 that is being produced in the reaction over time. This means that the amount of CO2 is increasing over time, presumably from zero. So your graph would start at zero (or no CO2) and increase over time (time on the x-axis).
The second thing to consider is whether the amount of CO2 being produced is consistent through out the reaction. Of course over time the amount of reactants you have is decreasing (because they are reacting) so the rate of the reaction should also decrease. This means your graph may be steeply rising to begin with when there are lots of reactants and lots of CO2 is being produced, and then over time the graph will become more shallow as the amount of CO2 being produced decreases.
On another point I have just noticed that your question states that the sodium bicarbonate is in excess and HCl is the limiting reagent so you should take this into accound with some of the other questions.
-
2.a) I agree the carbon dioxide would increase. So long as there was still HCl to react with it though. If HCl was the limiting reagent then this would not happen, but I think you assume HCl is in excess.
1. When excess lumps of sodium hydrogen carbonate are added to dilute hydrochloric acid the following reaction takes place.
NaHCO3(s) + HCl(aq) ----> NaCl(aq) + CO2(g) + H2O(l)
Outline two ways in which the rate of this reaction could be studied. In each case sketch a graph to show how the value of the chosen variable would change with time.
HCl is the limited reagent right from the start of the question. Throughout the question, the number of moles of carbon dioxide produced is fixed. Even if you add more lumps of sodium bicarbonate, you are going to get more carbon dioxide because there is limited amount of HCl present. The volume of carbon dioxide produced will be higher at higher temperature because the volume of a gas is directly proportional to its thermodynamic temperature.