Paper 2: 7.1 : Practical Flashcards
How can the rate of reaction be measured (3)
Measure change in mass
Measure the volume of gas produced (upside-down measuring cylinder or gas syringe)
Observe colour change/ precipitate formed
When can the change in mass be used to measure the rate of a reaction? Why?
When a gas is produced.
Gaseous molecules will be lost from the reaction vessel so fewer atoms in the reaction mixture.
Mass will decrease.
How do you calculate the rate of reaction?
Rate of Reaction =
Amount of product formed or reactant used Time
Marble chips are added to HCl. How can the rate of reaction be measured?
Measure the volume of gas produced (gas syringe or upside-down measuring cylinder) and record the time
Why must you be careful when measuring the volume of gas produced using a gas syringe?
You must ensure the volume produced will fit within the syringe otherwise it could damage the equipment and cause harm to the user
Why must the bung be immediately attached to the reaction vessel when measuring volume of gas produced?
To ensure minimal gas escapes
Name 3 ways the rate of reaction between HCl and marble chips could be increased
Increased surface area of marble chips
Increased concentration of acid
Increased temperature of reactants
Dilute HCl is added to sodium thiosulfate. How can the rate of reaction be measured?
Place piece of paper with a black cross below the reaction vessel and observe this cross through the solution
- Measure how long it takes for the cross disappear
Why is the precipitate rate experiment not very reliable?
It is very subjective - people might disagree over the exact point when the mark disappears or the solution changes colour
How can you determine the rate of a reaction at a particular time?
Plot results on a graph
Draw a tangent to the curve at this time
Calculate the gradient (change in y ÷ change in x)
Write a chemical equation for the reaction between HCl and marble chips (CaCO3)
2HCl + CaCO3 ⟶ H2O + CaCl2 + CO2
How do you know that a reaction is complete?
Mass of reaction mixture/ volume of gas/ colour remain the same
How does temperature affect the rate of a reaction? Why?
Increasing temperature increases the rate because particles have more kinetic energy so move faster (more frequent collisions) and more particles have energy above the activation energy (more collisions are successful).
How does concentration of reactants affect the rate of a reaction? Why?
Increasing concentration increases the rate because there are more particles in the same volume so there are more frequent successful collisions
How does pressure of reactants affect the rate of a reaction? Why?
Increasing pressure increases the rate because there are more particles in the same volume (or the same number of particles in a smaller volume) so there are more frequent successful collisions.
