Formulae, Equations And Amounts Of Substance

Question 1

What is Avagadro’s constant?

Answer 1

6.02 * 10^23

Question 2

What is a mole?

Answer 2

-The amount of substance that contains the same number of atoms or particles as 12g of Carbon-12
-It’s used because atoms are so small, it is very difficult to count the number of them accurately, so scientists use the mole to quantify them

Question 3

what is the molar mass?

Answer 3

-Molar mass is the atomic/formula/molecular mass
-The units are g/mol

Question 4

Acid + base/alkali = ?

Answer 4

Acid + base/alkali -> Salt +water

Question 5

Carbonates + acid = ?

Answer 5

Acid + Carbonate -> Salt + water + Carbon dioxide

Question 6

Acid + metal = ?

Answer 6

Acid + metal -> hydrogen + salt

Question 7

What are precipitation Calculations/reactions?

Answer 7

-Precipitation reactions are when we mix two solutions containing soluble ions and they form an insoluble compound

Question 8

Dm ^3 Conversions

Answer 8

-dm^3 = m^3 1000
-cm^3 = m^31000000

Question 9

How do you convert Celsius to Kelvin?

Answer 9

-You must add 273 ( ‘c + 273)

Question 10

Assumptions of an ideal gas

Answer 10

-We assume that the gas molecules are tiny compared to the spaces between them
-We also assume that there are no forces acting between the gas molecules
-We assume that the gas molecules move randomly
-Lastly, we assume that when the gas molecules collide, the collisions are elastic,
-Ultimately, there isn’t an ideal gas, but the equation above works well for many gases

Question 11

What is the Ideal gas equation?

Answer 11

-pV = nRT
-Pressure (Pa/kPa) * Volume (m^3) = moles (moles) * ideas gas constant (8.314 J/molK) * temperature (K)

Question 12

What is the Molar volume of gas?

Answer 12

-One mole of gas approximately has the volume of 24dm^3 at room temperature and pressure

Question 13

What is the equation linking amount of moles, the molar volume of gas and volume?

Answer 13

Amount of substance (mol) = Volume (dm^3)/24

Question 14

What is the equation linking amount of substance, mass and molar mass?

Answer 14

Amount of substance (mol) = mass(g)/Molar mass (g/mol)

Question 15

What is the empirical formula?

Answer 15

-The molecular formula tells us the elements in a molecule and the number of atoms of each element; e.g. methane = CH4
-The empirical formula tells us the simplest whole-number ratio of the atoms of each element in a compound
-To work out empirical formula, we first list the mass of each elements , Then figure the moles by dividing by Ar
-Next we divide by the smallest number of moles given in ratio
-And then we round up or down, giving the ratio of 1:2
-Now we write this ration into the empirical formula, which gives us CH2
-In the case of decimals, we must multiply until all the digits are whole numbers

Question 16

What is Atom economy?

Answer 16

-The atom economy tell us what percentage of the mass of the reactant atoms end up in the product we want
-The equation for this is as follows:

Atom economy = (molecular mass of desired product / sum of molecular masses of all the reactants) *100

-reactions with a high atom economy are more sustainable than reactions with a low atom economy because less of the mass reactants end up in waste products
-Other factors need to be considered too, such as energy use. For example, a reaction with high atom economy but requires high energy may be less sustainable
-Also the waste product may be used by a chemical producer as the starting material for a different reaction, increasing overall sustainability

Question 17

What is Percentage yield?

Answer 17

-In a reaction it is very unlikely than well get 100% yield for numerous reasons
-for example, not all the reactant may react, sometimes side reactions take place making different products and sometimes some of our product may be lost in e.g filtration
-The equation for percentage yield is as follows:

Yield(%) = (Yield (mass provided) / Maximum theoretical yield (found using reacting mass calculation)) *100

-The yield and maximum theoretical yield can both be in grams or moles
-We can find the maximum theoretical yield via the reacting mass calculation

Question 18

What is accuracy?

Answer 18

-Closeness of agreement of results
-Accurate results are close to the accepted value

Question 19

What is error?

Answer 19

-Difference between individual measurements and accepted values

Question 20

What is uncertainty?

Answer 20

-Range of Values within the measurement lies

Question 21

What is concordant values?

Answer 21

-Values that agree with each other
-Within 0.1cm^3 of each other

Question 22

How would i calculate error?

Answer 22

-Measuring equipment typically has uncertainty, or how sensitive it is to providing the accurate value - it is typically hard the smallest value on the scale
-The equation as follows is used to figure out uncertainty :

Error = Measured value - actual value

Error/actual value * 100 = % of error

Question 23

How can I calculate uncertainty

Answer 23

-Uncertainty is the value given following a plus and minus sign, e.g, the uncertainty of a scale is +/- 0.005g

Uncertainty/value recorded *100 = % uncertainty

-The uncertainty value is doubled if a reading is taken twice, e.g in a change in value

Question 24

Give the equation linking number of moles, mass and molar mass

Answer 24

Mass = Mr*mol

Question 25

What is the equation to calculate concentration?

Answer 25

-Concentration = number of moles / Volume
-c (mol dm^3) = n (mol) / V (dm^3)