Topic 3 - Quantitative chemistry

Question 1

What is the equation to find out Relative atomic mass of isotopes?

Answer 1

(mass no of isotope 1 x %abundance of isotope 1) + (mass no of isotope 2 x %abundance of isotope 2)
100

Question 2

What is relative atomic mass

Answer 2

The average mass of all the isotopes of an element compared with the standard carbon atom.

Question 3

What is the relative formula mass (Mr) of H2SO4?

Answer 3

98

Question 4

Fill the blanks:

Isotopes are atoms of an element that have the same number of _______ but different number of ________.

Answer 4

1. protons
2. neutrons

Question 5

what is the equation for finding the Percentage my mass of an element?

Answer 5

Ar of element x number of atoms x100
Mr of compound

Question 6

What is the equaion for finding the moles of a substance?

Answer 6

moles = mass (g) / relative formula mass (Mr)

Question 7

Fill in the blanks:

A mole of a substance is the relative atomic ____ or formula mass in _____

Answer 7

1. mass
2. grams

Question 8

36g of carbon = …

Answer 8

3 moles

Question 9

2 moles of CO2=…

Answer 9

88g

Question 10

Avagadro’s constant:
1 mole= ….

Answer 10

6.02 x 10^23

Question 11

How many atoms are in 2 moles of carbon?

Answer 11

1.204 x 10^24

Question 12

How many particles are in 46g of sodium

Answer 12

1.204 x 10^24

Question 13

What is yield?

Answer 13

the amount of product made from a chemical reaction

Question 14

What is theoretical yield?

Answer 14

the amount of product that is expected to get

Question 15

What is actual yield?

Answer 15

the yield that you actually made

Question 16

What is the formula for percentage yield?

Answer 16

percentage yield = (actual yield/ theoretical yield) x 100

Question 17

Why is yield never 100%?

Answer 17

• some products get lost into the surroundings
• not all the reactants will react to form products

Question 18

Fill in the blanks:
If a reaction produces only one product then the atom economy is __%

Answer 18

100

Question 19

What is the equation to find out atom economy?

Answer 19

atom economy= (mass useful products/ mass of all products) x 100

Question 20

What is the equation to find out concentration?

Answer 20

concentration (mol/dm^3)= moles / volume (dm^3)

Question 21

What is titration?

Answer 21

A technique used to measure accurately what volumes of acid an alkali completely react together.

Question 22

What is titration used for?

Answer 22

to find the concentration of an unknown substance

Question 23

What is the endpoint of a reaction?

Answer 23

the point when a reaction is complete
(an indicator is used to judge the endpoint)

Question 24

What is the meniscus?

Answer 24

The curved surface of the solution

Question 25

How would you carry out a titration calculation?

Answer 25

1. place 25cm^3 of an alkali (or acid) into a conical flask using a pipette.
2. place acid (or alkali) into a burrette
3. add indicator to the flask
   4.slowlt add the solution from the burrette, swirl and add dropwise near the end, until the endpoint is reached (the colour changes)
4. Note the final recording
5. repeat until you get concordant results (2 or 3 titres that are within 0.1cm^3)

Question 26

What is the equation for finding the moles of a gas?

Answer 26

mole of gass=volume of gas (dm^3) / 24dm^3

Question 27

Fill in the gaps:
one mole gas occupies the same volume at room _____________ and ____________
1 mole of gas= __dm^3

Answer 27

temperature
pressure
24