Topic 5- Formulae, Equations, Amount of substances
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- Created by: McTighe
- Created on: 13-02-18 17:34
What is the amount of a substance measured in?
Moles
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What is the relative atomic mass?
The average mass of all isoptopes in an element, in relation to 1/12th of the mass of an atom of the isotope carbon-12
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What is the molar mass?
The mass per one pole of the substance (g/mol)
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How do you work out the number of moles?
Mass of substance (g)/Molar mass (g/mol)
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What is the Avogardo constant?
The number of atoms per mole
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What number is the avogardo constant?
6.022 X 10^23 atoms
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What is the Empirical formula?
The simplest whole number ratio of the atoms of different elements in a compund
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What is the empirical formula of Iron bromide, if it contains 3.8g of Fe and 16.3g of Br
Fe= 3.8/55.8=0.068 Br= 16.3/79.9=0.204 0.068:0.204 1:3 = FeBr3
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What is percentage composition?
The percentage by mass of each of the elements in a sample of a compound
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What is the molecular formula?
The actual number of atoms of each element in a molecule
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How do you work out the molecular formula?
Find empirical formula. Divide mass by empirical formula atomic mass to find how many tuimes you need to times it by.
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What is an ideal gas?
GAses which obey gas laws perfectly. Real gases do not obey the laws under all conditions. Under laboratory conditions, gases behave closely like an ideal gas
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What is the ideal gas equation?
PV = nRT
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What type of units is the ideal gas equation using?
SI Units (Internationally agreed units for measurements in science)
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What is pressure measured in?
Pascals (Pa) One newton per square meter
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What is volume measured in?
Cubic meters (m^3)
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What is temperature measured in?
Kelvin (K) (0K=-273*C)
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What is the universal gas constant (R)?
8.31 Jmol-1K-1
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What is a full balanced equation?
A equation that includes all reactants and products of a reaction, and includes state symbols. It has same number of atoms of each element of both sides
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What is an ionic equation?
An equation which includes all charges on reactants and products, where the charges balance
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What is the molar volume?
The volume of 1 mol of the gas under stated conditions: Room temp (approx 16*C), atomspheric pressure (100Kpa). The molar volume is 24.0dm^3mol-1
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What is the equation to work out the volume using dm^3
Number of moles X 24
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What is the equation to work out the volume using cm^3?
Number of moles X 24000
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What is concentration?
How much solute is dissolved in a certain volume of a solution
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How do you work out concentration?
Moles/Volume
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What is a titration?
A volumetric analysis technique for finding the concentrations of solutions and for investigating the amount of chemicals involved in a reaction
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What is needed to be made before a titration can occur?
A standard solution
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Why are standard solutions important?
They are important in checking and calculating instrumental methods.
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What is a standard solution?
A solution with an accurately known concentration
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What is a mean titre of a titration?
The mean of two concordant results (within 0.05cm^3 of each other)
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What two indicators can be used for a titration?
-Methyl orange -Phenolphthalein
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How is a standard solution made?
1.Weigh solid in tub, tip in beaker, reweigh tub 2.Dissolve solute in solvent with stirring rod 3.Transfer solution into volumetric flask, rising stirring rod/beaker and pour in flask 4.Fill flask so menicus on graduation mark (use pipette)
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When are standard solutions appropriate to be used?
-When very pure -Does not gain/lose mass in air -Has high molar mass so weighing errors are minimised
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What are these standards called?
Primary standards
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What is a primary standard?
A chemical which can be weighed out accurately to make up a standard solution
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Give two reasons why a solution is diluted
1.To make solution with concentration needed for particular experiment 2.To dilute an unknown sample for analysis to give concentration in a titration
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What is the end point?
Where a titration reaches a pint where the colour changes, showing that enough of the solution in the burette has been added to react with the chemical in the flask
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What is the equivalence point?
The point reached when the amount of reactant added for a burette is enough the react with all the measured amount of chemical in the flask
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What is a strong acid?
A acid which is fully ionised in solution
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What is a weak acid?
A acid which is partially ionised in solution
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What is accuracy?
How close the measurement is to the true value
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What uncertantites are found in a titration?
-Difficult to measure volume of liquid when meniscus between two graduation marks -Material may not be 100% pure -Burette may be calibrated at different temp -Difficult to judge end point -Balance only shows to number of decimal places
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What is precision?
How close the measurements are together. They may have small random errors
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What is a systematic error?
An error which differs from the true value by the same amount each time
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What does bias mean?
Arises from systematic errors which affects all measurements in the same way, making them high/lower than true value
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What is a yield?
Uses to assess efficiency of a chemical process. The actual yield is the mass of product. The theoretical yield in the mass obtained if the reaction goes according to equation
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How do you work out the percentage yield?
Actual yield/Theoretical yield X100%
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Why may the percentage yield not be 100%?
-Reactants may not be 100% pure -Some products may be lost during transfer of chemical -May be side reactions when reactants form different products -Some reactants may not react as it is too slow/reach equilibrium
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What is atom economy?
A reaction calculated from balanced equation to show the percentage of mass of the atoms in the reactants that is converted to the desired products
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How do you work out atom economy?
Molar mass of desired product/Molar mass of all products X 100%
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Give two types of qualitative testing used in chemistry
-Flame tests -Test-tube experiments
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What is an ionic precipitation reaction used for?
To test for negative ions
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Give an example of an ionic precipitate?
-Add silver nitrate to halides
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Give an example of a Acid-Base reaction
Hydrochloric acid to carbonate adds hydrogen ions turning into carbonic acid molecules which decompose to water and co2
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What can be used to identify the gas given off contains a carbonate?
Lime water
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What is redox (displacement reaction)
Where a reaction involved reducing and oxidising
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Give examples of common agents used in inorganic tests
Chlorine, Bromine, Acidic solution of iron, maganate or dichromate ions
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What colour does colourless iodine ions turn when it is oxidised?
Yellow-Brown
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Other cards in this set
Card 2
Front
What is the relative atomic mass?
Back
The average mass of all isoptopes in an element, in relation to 1/12th of the mass of an atom of the isotope carbon-12
Card 3
Front
What is the molar mass?
Back
Card 4
Front
How do you work out the number of moles?
Back
Card 5
Front
What is the Avogardo constant?
Back
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