A student had calculated the theoretical yield of a product was 8 g. The actual yield obtained was 6 g. What was the percentage yield?
48%
75%
133%
Which of the following could explain why the percentage yield in a chemical reaction was less than 100%?
Some of the product was lost during pouring liquids
The reaction forms more than one product
The top pan balance was faulty
What name is given to the chemicals that are produced in a reaction which are not the desired product?
By-products
Impurities
Reactants
The Mr of the desired product in a reaction is 95. The sum of the Mr values for the reactants is 113. What is the atom economy for this reaction?
84%
135%
107%
Which of the following would increase the effective atom economy for a reaction?
Increasing the temperature
Using a catalyst
Selling the by-product for additional profit
In an acid-alkali titration, which piece of apparatus is used to measure exactly 25.0 cm3 of alkali into the conical flask?
Measuring cylinder
Pipette
Burette
In a titration, the first titre value was 23.50 cm3. The next few titre values were 22.40, 22.80 and 22.90. Which two values should be used to calculate the average titre?
23.50 and 22.90
22.80 and 22.90
22.40 and 22.90
Which part of the meniscus should be used when reading the volume of liquid in the burette?
The lowest part of the meniscus
About halfway up the meniscus
The highest part of the meniscus
Why is it important to place the conical flask on a white tile when doing a titration?
Because it prevents acids and alkalis getting onto the lab bench
Because it insulates the lab bench from getting too hot
So that the colour change of the indicator is easier to see
What is the most sensible safety precaution when doing an acid-alkali titration?
Wear safety spectacles
Stay away from flames and sources of ignition
Do not pour chemicals down the sink