1.2 Amount Of Substance Part 2 Flashcards
What does the stochiometry tell you about a reaction?
The relative number of moles and reactants and products involved in a reaction
How is the stoichiometry found?
By writing a balanced symbol equation
What mass of magnesium oxide is produces when 25.0g of magnesium carbonate is heated?
12.0g
What mass of sodium chloride is produced when 10.0g of sodium carbonate reacts with excess hydrochloric acid?
11.1g
Calculate how many kilograms of calcium carbonate must be heated in order to produce one kilogram of calcium oxide
1.8kg (moles of CaO = 17.8mol)(balanced equation)(mass of CaCO3)
1) Write the equation for the reaction between magnesium carbonate and nitric acid.
1. 00g of MgCO3 is reacted with excess nitric acid.
a) Calculate the moles of MgCO3 which reacted
b) Hence, state the moles of CO2 formed
c) reacting at 25C and 100kPa, work out the volume of CO2 produced in cm3 (R= 8.3144)
1) MgCO3 + 2HNO3 -> Mg(NO3)2 + CO2 + H2O
a) 0.0119
b) 0.0119
c) 2.95 x102
At 20C and 98kPa, 440cm3 of hydrogen gas is recovered form a piece of lithium fully reacting with water.
Work out the mass of the piece of lithium (R=8.3144)
0.24g
How do you make a standard solution?
- Dissolve a known mass of solid in de-ionised water
- Using a funnel, transfer into a volumetric flask, including washings
- Make up to the graduated line by carefully adding de-ionised water, making sure the meniscus sits in the line
- Stopper the flask and invert to mix the contents thoroughly
How do you find the concentration of a solution of a base?
- Fill a burette with a known concentration of the acid
- Add a known volume of base into a conical flask
- Add a few drops of indicator to the base in the flask
- Add the solution of the acid from the burette until the indicator just changes colour. This is know as the end point
- Record the volume of acid added: record your burette readings to the nearest 0.1cm3
- Perform a rough titration and then sufficient accurate ones until the titres are concordant
- Calculate the mean titre from the concordant titres
What colour is methyl orange in acid?
Pink
What colour is methyl orange in a base?
Yellow
What is the end point colour of methyl orange?
Orange
What colour is phenolphthalein in acid?
Colourless
What colour is phenolphthalein in a base?
Pink
What is the end point colour of phenolphthalein?
Either colourless or pink depending on what the start colour was
25.0 cm3 of sodium hydroxide required 21.5 cm3 of 0.100 moldm-3 hydrochloric acid for neutralisation. Calculate the concentration of NaOH
0.0860 moldm-3
25.0cm3 of 0.020 moldm-3 sodium hydroxide required 28.2 cm3 of sulfuric acid for neutralisation. Calculate the concentration of the sulfuric acid.
8.87 x10-3 moldm-3
12.5 cm3 of 0.015 moldm-3 sulfuric acid was neutralised by potassium hydroxide with a concentration of 0.025 moldm-3. Calculate the volume, in cm3, of potassium hydroxide required.
15.0 cm3
1.32g of an acid HX was dissolved in water and made up to 250 cm3 in a volumetric flask. 25.0cm3 of this solution required 22.0cm3 of 0.100 moldm-3 sodium hydroxide for neutralisation.
HX(aq) + NaOH -> NaX(aq) + H2O(l)
a) Calculate the amount of moles of NaOH needed to neutralise 25.0 cm3 of HX
b) Using the balanced equation, write down the amount of moles of HX used in the titration
c) Calculate the moles of HX in 250 cm3 of the acid solution
d) Calculate the molar mass of HX.
a) 2.2 x10-3
b) 2.2 x10-3
c) 2.2 x10-2
d) 60.0 gmol-1
2.13 of a carbonate M2CO3 was dissolved in water and made up to 100 cm3 in a volumetric flask. 10.0cm3 of this solution required 18.50cm3 of 0.1 moldm-3 hydrochloric acid for neutralisation.
2HCl + M2CO3 -> 2MCl + H2O + CO2
a) Calculate the amount in moles of HCl needed to neutralise 10.0cm3 of the carbonate solution
b) Using the equation, write the amount of M2CO2
c) Calculate the amount of moles of M2CO3 in 100 cm3 of the carbonate
d) Calculate the molar mass of M2CO3
e) calculate the relative atomic mass of M
f) Use the periodic table to identify M
a) 1.85 x10-3
b) 9.25 x10-4
c) 9.25 x10-3
d) 230.3 gmol-1
e) 85.2
f) Rb
What is a hydrated salt?
A salt which contains water
What happens when hydrated salts are heated?
The water is evaporated and the compound is said to be anhydrous
How do you calculate the number of moles of water of crystallisation?
- You need the masses of the hydrated and anhydrous salts
- Mass of water = mass hydrated salt - mass anhydrous salt
- Work out the number of moles of anhydrous salt and water
- Find the simplest whole number ratio
6.95g hydrated iron(ll) sulfate, FeSO4.xH2O was heated to constant mass. 3.80g anhydrous salt remained. Calculate the number of moles of water of crystallisation
FeSO4.7H2O
27.93g of hydrated sodium carbonate Na2CO3.xH2O was dissolved in water and made up 1000 cm3 in a volumetric flask
2HNO3 + Na2CO3 -> 2NaNO3 + H2O + CO2
Calculate x in the formula Na2CO3.xH2O
Na2CO3.10H2O
How do you calculate percentage yield?
(Actual yield / theoretical yield) x 100
What is the theoretical yield of a reaction?
The number of moles expected if the reactants were completely converted into products
What is the actual yield of a reaction?
The actual number of moles of product formed in the reaction
Ethanol, CH3CH2OH, can be oxidised to form ethanoic acid CH3COOH.
CH3CH2OH + 2(O) -> CH3COOH + H2O
In an experiment, 2.30 ethanol was oxidised to produce 2.01g ethanoic acid.
Calculate the percentage yield?
67%
What are the reasons for low percentage yield?
- Lost some substances in transfers
- Lost some substances in purification
- Reaction may not go to completion
- Extra byproducts may be created
Calcium carbonate decomposes on heating to give calcium oxide and carbon dioxide.
If 12.4g of calcium carbonate are heated with a 90% conversion into products, calculate the mass of calcium oxide made
6.28g
What is atom economy?
It is a measure of the efficiency of a reaction in terms of the atoms involved
How do you calculate the atom economy for a reaction?
(Molecular mass of desired product/ sum of molecular mass of all products) x100
Calculate the atom economy for the preparation of propan-1-ol, CH3CH3CH2OH, from the hydrolysis of 1-bromopropane, CH3CH2CH2Br.
CH3CH2CH2Br + NaOH -> CH3CH2OH + NaBr
What is the significance of this value in terms of the environment?
36.8%
60+% of the mass of reactants is waste. Wasted raw materials and energy
What is a major factor in the atom economy value?
Type of reaction
How does the type of reaction affect the atom economy value?
Addition- atom economy 100%
Substitution/elimination - less than 100%
Calculate the atom economy value for the preparation of ethanol by the hydration of ethene
100% - addition reaction
Calculate the atom economy value the preparation of the ethanol by the reaction of chloroethene with aqueous sodium hydroxide
44.0% - substitution
Calculate the atom economy value for the preparation of ethanol from carbohydrates such as glucose
51% - decomposition
How can you improve chemical sustainability? (9)
- Reduce the use of hazardous chemicals
- Reduce the amount of waste
- Recycle the waste
- Use fewer chemicals
- Design for energy efficiency
- Use renewable feedstocks
- Manufacture biodegradable products
- Think Safety
- Establish international co-operation
What are the downsides to green chemistry?
- Cost
- Reduction of land needed for food
- Adhering to international agreements
