Quantitative Chemistry 1
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In a balanced equation what must the Mr on each side be?
Equal
What is empirical formula?
Simplest whole number ratio of atoms of each element in a compound e.g. C6H12O6. LCM is 6 so divide by 6 leaving you with CH2O
How do you figure out the chemical symbol of a compound when you are given the percentages the elements within it?
Divide the percentage of each element by their Mr, then divide all the numbers why the smallest number present. The answer gives you the ratio For example, 11.6% of nitrogen and 88.4% of chlorine. 11.4/14 and 88.4/35.5 is 0.8286 and 2.4901. Divide both numbers by 0.8286 to get 1 and 3. The answer is NCl3
What are covalent compounds made out of?
Non-metals
What is an ionic compound?
Chemical compound formed when a metal transfers electrons to a non-metal, producing oppositely charged ions
What must the charges of ionic compounds be?
Balanced Na+ and Cl- form NaCl Ca(2+) and Cl(-) form CaCl2 as 2 Cls are needed to balance the equation
What are the steps to write half-equations?
Write unbalanced half equation, balance all the atoms except hydrogen and oxygen (if present), if needed then balance oxygen with H2O and hydrogen with H(+), balance charges using electrons (e-) Iron (II) oxidises into Iron (III). Fe (2+) becomes Fe (3+) + e-
What has happened if the electron is added to the right in a half equation?
Oxidation, electrons have been lost
What has happened if the electron is added to the left in a half equation?
Reduction, electrons have been gained
What are the state symbols?
s-solid, particles are tightly packed and fixed in shape l-liquid, pure liquid substance g-gas, particles are far apart and move freely aq-aqueous, dissolved in water and substance is in a solution
What state are dissolved ionic compounds?
Aqueous
What state are undissolved ionic compounds?
Solid
What is Avogadro’s constant?
Number of particles in 1 mole, 6.02 times 10(tothepowerof23)
What is a mole?
SI unit for amount of substance
What is molar mass?
1 mole of a substance
What is the unit of molar mass?
g/mol
What is the formula for moles?
Mass/Mr
What is the law of conservation of mass?
Mass can’t be created or destroyed. In a closed system, the total mass stays constant in a chemical reaction and the atoms are simply rearranged.
What can substances do in an open system and what is the effect on the measured mass?
Enter or leave the reaction space, especially gases as their particles move quickly and are uncontained. The measured mass seems to decrease if they leave and increase if they enter. Solids and liquids stay in the container
What is stoichiometry?
Ratio of moles of reactants and products in a chemical equation
What is a limiting reactant?
Reactant that is completely used up first in a chemical reaction
What happens to a chemical reaction once the limiting reactant runs out?
The reaction stops
What is theoretical yield?
Maximum possible mass of reactant
What is the formula for percentage yield?
Actual yield/theoretical yield x 100