Quantitive Chemistry

Question 1

what is Avogadro’s constant?

Answer 1

6.02 x 10^23

Question 2

what is the formula for moles?

Answer 2

mass / RFM

Question 3

what is the formula for mass (moles)?

Answer 3

moles x RFM

Question 4

how many moles are there in 42.5g of ammonia?

Answer 4

moles = 42.5 / 17 (RFM of ammonia)
= 2.5 moles

Question 5

what is the mass of 3 moles of carbon dioxide?

Answer 5

mass = 3 x 44 (RFM of CO2)
= 132g of CO2

Question 6

what does the term ‘limiting reactants’ mean?

Answer 6

when one of our reactants have been used up, and can no longer react

Question 7

calculate the mass of NA^2O produced when 115g of Na is burned in air

Answer 7

1 - moles of Na = 115 / 23 = 5
2 - (equation 4Na + O^2 —> 2Na^2O)
ratio Na : Na^2O = 2 : 1
5 : 2.5
3 - mass Na^2O = 2.5 x 62 (RFM of Na^2O) = 155g

Question 8

what is the equation for concentration (moles)?

Answer 8

moles / volume

Question 9

what is the equation for volume (moles)?

Answer 9

moles / concentration

Question 10

800cm^3 of sodium hydroxide at a concentration of 0.2 mol/dm^3. how many moles?

Answer 10

moles = conc. x vol.
800cm / 1000 = 0.8dm
= 0.8 x 0.2 = 0.16moles

Question 11

what is the equation for mass in concentration of solutions?

Answer 11

concentration x volume

Question 12

what is the equation for concentration in concentration of solutions?

Answer 12

mass / volume

Question 13

what is the equation for volume in concentration of solutions?

Answer 13

mass / concentration

Question 14

40g of NaOH dissolved in 2.5dm^3 of water. what is the concentration?

Answer 14

40 / 2.5 = 16g/dm^3

Question 15

24g copper sulphate in 480cm^3 of water. what is the concentration?

Answer 15

480cm^3 / 1000 = 0.48dm^3
24 / 0.48 = 50g/dm^3