elements of life 6 questions Flashcards
0.84 g of magnesium was burnt in 0.56 g of oxygen. What is the formula of the magnesium oxide produced?
Mol Mg = 0.84 / 24 = 0.035 mol
Mol O = 0.56 / 16 = 0.035
1 : 1 so MgO
Experimental results that a hydrocarbon is 75% carbon and 25% hydrogen, by mass. Derive its empirical formula.
Let mass of hydrocarbon = 100 g
Mol C = 75 / 12 = 6.25 mol
Mol H = 25 / 1 = 25 mol
C : H = 1 : 4 so CH4
Calculate the mass of aluminium oxide formed when 135 g of aluminium is burned in air.
4Al + 3O2 →2Al2O3
Mol Al = 135 / 27 = 5 mol
Mol Al2O3 = 5 x 2/4 = 2.5 mol
Mass Al2O3 = 2.5 x 102 = 255 g
2.53 g of hydrated magnesium chloride, MgCl2 * xH2O, was heated to constant mass. 1.17 g of solid remained.
What is the formula of the hydrated compound?
Mol pure solid = 1.17 / 95.3
Mass water in salt = 2.53 - 1.17 = 1.36 g
Mol water = 1.36 / 18
Mol salt to water in ratio 1 : x = 1 : 6.15
Formula = MgCl2 * 6H2O
What is the volume of 319.5 g of chlorine at room temperature and pressure?
Volume = mol x 24
= (319.5 / 35.5 x 2) x 24 = 108 dm3
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0.84g of magnesium was burnt in excess oxygen, producing 1.1g of mg oxide. work out the percentage yield of the reaction :
- write a balanced equation for the reaction
2Mg (s) + O2 - 2MgO (s) - calculate the amount of substance, in moles of mg
0.84g/24gmol-1 = 0m035mol - The balanced equation tells us that the ratio of Mg to MgO produced is 2:2 or 1.1 - means the max amount of mgoxide = produced from mg is 0.035mol
- Calculate the formula mass of MgO
Ar(Mg) = 24; Ar(o) =16 Mr(MgO) = 40 - The experiement produced 1.1g calculate the percentage yield
1.1g/1.4g x 100 = 79% (2.s.f)
2.23g of hydrated mag chloride, MgCl2*xH2o, *was heated to constant mass. 1.17g of solid remained. what is the formula of the hydrated compound?
- calculate the mass of water in 2.53g MgCl2 2.53-1.17g = 1.36g
- calculate the number of moles of water
1.36/18 = 0.076 mols - cal num of mol of MgCl2 in the anhydrous solid (Mr MgCl2= 95.9 ) 1.17/95.9 = 0.012 mols
- cal moles then divide by the lowest num
1 : 6.3 - MgCl2*6H2O
what is the balanced equation fo reaction between calcium and water :
- Calcium(s) + water (l) = Ca(OH)2 (aq) + H2(g)
Find the emprical formula of iodine oxyden
- g/ 126.9 = 0.1 4.0g/16.0 =2.5
- 0.1/0.1 0.25/0.1 =2.5
- 2:5
- empirical formula of the compound is I2O5
Explain the formation of calcium carbonate:
Thhe increase of carbon dioxide in the sea means more gas is dissolved in the sea water. This lowers the pH of the sea and could result in the calcium carbonate shells.
Explain the formation of salts:
The reaction of carbonate ions with acids to form salts is an example of a neutralisation reaction.
What happens when acid and metal reacts together:
Salt is formed
- formula: H2SO4 (aq)+ Mg(s) =MgSO4(aq) + H2 (g)
2.sulfuric acid + magnesium metal = magnesium sulfate** (salt)** + hydrogen - They are used as bath salts
- MgSO4
hydrochloric acid + lithium oxide
- formula equation - word equation - their use - salt
- formula: Li2O + HCl = LiCl + H2O
- lithium oxide + hydrochloric acid = lithium chloride + water
- They are used as lithium chloride
- LiCl
barium chloride + magnesium sulfate
- formula equation - word equation - their use -salt
- MgSO4(aq) + BaCl2(s) = BaSO4 (s) + MgCl2 (aq)
- barium chloride + magnesium sulfate = barium sulfate + magnesium chloride
- it is used as “barium meal” which shows up soft tissues on X-ray
- Barium sulfate (BaSO4) = salt
