Quantitative Chemistry

Question 1

Concentration definition

Answer 1

A measure of how much of a substance is dissolved in a known amount of water

Question 2

What is the volume of one mole of any gas at room temperature and pressure

Answer 2

(20°C and 1 atmosphere pressure) is 24 dm3;

Question 3

Molar gas volume

Answer 3

The volume of one mole of gas under specified conditions of temperature and pressure

Question 4

Equation for number of moles of gas

Answer 4

N = V
——
Vm

Question 5

Avogadro’s Law states:

Answer 5

Equal volumes of gases at the same temperature and pressure contain the same number of particles/molecules

Question 6

Atom economy

Answer 6

atom economy =
mass of desired product x 100
total mass of products

Question 7

Why is a high atom economy important (2)

Answer 7

• Most of the mass of the reactants ends up in the desired product and therefore there’s less waste
• the less waste material that is produced in any industrial process the more sustainable it is and also the more economical it is as there is less waste to dispose of

Question 8

Preparation of the burette (4)

Answer 8

• rinse with deionised water
• Rinse with solution to be used in the burette and ensuring the solution goes through the jet
• Fill with solution, ensuring the jet is filled and there are no air bubbles
• Allow solution to run out until the bottom of the meniscus is on the zero line

Question 9

Preparation of Pipette (4)

Answer 9

• Rinse with deionised water
• Rinse it with the solution to be used in the Pipette
• holding the Pipette vertically with the volume line at eye level, use a Pipette filler to draw up the solution and run out the solution until the bottom of the meniscus is on the line
• release the solution into a conical flask, touching the tip of the Pipette onto the surface of the solution

.

Question 10

What are concordat results

Answer 10

Results that differ by less than 0.10cm3

Question 11

How can the volumes of acid and alkali solutions that react together be measured ?

Answer 11

By titration using phenolphthalein or methyl orange

Question 12

Reactions of acids and alkalis in phenolphthalein or methyl orange

Answer 12

Phenolphthalein:

• If acid is being added to alkali, phenolphthalein turns from pink to colourless
• If alkali is being added to acid, phenolphthalein turns from colourless to pink

Methyl orange:

• If acid is being added to alkali, methyl orange changes from yellow to red
• If alkali is being added to acid, methyl orange changes from red to yellow

Question 12

Standard solution definition

Answer 12

A standard solution is a solution of known concentration

Question 12

How is accuracy in determining the end point in titration obtained? (3)

Answer 12

How is accuracy in determining the end point in titration obtained? (3)

• Adding The solution in the burette dropwise near the end point
• reading the burette volume at the bottom of the meniscus
• swirling the conical flask during the titration to ensure mixing is complete
• rinse with deionised water
• Rinse with solution to be used in the burette and ensuring the solution goes through the jet
• Fill with solution, ensuring the jet is filled and there are no air bubbles
• Allow solution to run out until the bottom of the meniscus is on the zero line

Question 12

Reliability in titration

Answer 12

• Titration is Repeated to obtain concord ant results (usually within 0.1cm)