Quantitative chemistry Flashcards
What is the mass of one mole of a substance, in grams, equal to?
The relative formula mass of the substance
How many moles are in 46 g of CaO?
Relative molecular mass = ( 40 x 1 ) + ( 16 x 1 )
Moles = 46 g / 56 = 0.82 moles
Calculate the concentration of sodium hydroxide solution when 44 g of sodium hydroxide is dissolved in 0.5 dm3 of water.
44 g / 0.5 dm3 = 88 g / dm3
Calculate the relative formula mass (Mr) of CaO
Relative atomic mass Mg = 24; Cl = 35.5; Ca = 40; O = 16; Al = 27
CaO: (40 x 1) + (16 x 1) = 56
How many atoms are in Al2O3?
Five atoms - two aluminium and three oxygen
How many elements are in H2SO4?
Three elements - Hydrogen, sulfur and oxygen
Calculate the relative formula mass (Mr) of MgCl2
Relative atomic mass Mg = 24; Cl = 35.5; Ca = 40; O = 16; Al = 27
MgCl2: (24 x 1) + (35.5 x 2) = 95
How many atoms are in H2SO4?
Seven atoms - two hydrogens, one sulfur and four oxygens
A piece of magnesium is added to the acid. What would happen to the mass reading on the balance and why?
It would stay the same because there is a lid on the conical flask so no gas can escape.
Calculate the relative formula mass (Mr) of Al2O3
Relative atomic mass: Mg = 24; Cl = 35.5; Ca = 40; O = 16; Al = 27
Al2O3: (27 x 2) + (16 x 3) = 102
What does the law of the conservation of mass state?
No atoms are lost or made during a chemical reaction
Calculate the concentration of sodium hydroxide solution when 3.5 moles of sodium hydroxide is dissolved in 100 cm3 of water. Give your answer in mol/dm3.
Convert volume of water to dm3 100 cm3 / 1000 = 0.1 dm3
3.5 moles / 0.1 dm3 = 35 mol/dm3
Describe the equation is words in terms of the number of moles of each substance reacting.
H2SO4 + 2 NaOH → Na2SO4 + 2 H2O
One mole of sulfuric acid reacts with two moles of sodium hydroxide to produce one mole of sodium sulfate and two moles of water.
Why is one reactant often added in excess to a reaction?
To ensure that all of the other reactant is used up.
Calculate the percentage mass of hydrogen in sulfuric acid (H2SO4). Give your answer to the nearest whole number.
Relative atomic masses: N = 14 ; H = 1 ; S = 32 ; O = 16.
( 1 x 2 ) x 100
( 1 x 2 ) + ( 32 x 1 ) + ( 16 x 4)
= 2 %
What equation links concentration, number of moles of solute and volume of solvent?
Calculate the percentage mass of hydrogen in ammonia (NH3). Give your answer to the nearest whole number.
Relative atomic masses: N = 14 ; H = 1 ; S = 32 ; O = 16.
( 1 x 3 ) x 100
( 14 x 1 ) + ( 1 x 3 )
= 17.6 = 18 %
What equation links concentration, mass of solute and volume of solvent?
A piece of magnesium is added to the acid. What would happen to the mass reading on the balance and why?
It would decrease because there is no lid on the conical flask so gas can escape and therefore mass is ’lost’ from the flask.
How many moles are in 50 g of O2?
Relative molecular mass = ( 16 x 2)
moles = 50 g / 32 = 1.6 moles
Calculate the mass of CO2 produced when 50 g of CaCO3 is thermally decomposed.
CaCO3 → CaO + CO2
