Quiz 2 & 4

Dimensional Analysis Formula:

Measurement x (Top (The Element You want))

----------------------------————————

(Bottom (Element You want to get rid of))

How to measure precision?

Go as many decimal places as the instrument allows. Add another decimal point if you’re estimating between the lines.

What should you do

Always write your units

Moles —> Grams (Formula)

mol (of element) x molar mass (of element)

Grams —> Moles (Formula)

mass (of element) (grams)

———————————-

molar mass

1 mol = ?

22.4 L

What is Molar mass

1 mol of an element

Mol —> Mol (Formula)

(x mol a = y mol b) (x and y = coefficients of a balanced chemical reaction

Given Mol x Desired Mol (mol ratio)

——————————-- = Desired Mol

Given Mol (mol ratio)

Mol —> Particles

Mol x 6.02 × 10^23 (Avogadro number)

Mass to Mass calculations

Starting Weight → Convert to Mol → Multiply by Molar Ratio → Convert back to grams

\text{g A} \times \frac{1 \text{ mole A}}{\text{molar mass } (\text{g}) \text{ A}} \times \frac{\text{Y mol B}}{\text{X mol A}} \times \frac{\text{molar mass } (\text{g}) \text{ B}}{1 \text{ mol B}}

What is the molar ratio?

Coefficients from balanced reaction of reactants and products in a chemical reaction.

Molar Ratio here

1 : 3 : 2

First step of mass to mass calculation

Convert given mass to moles

Second step of mass to mass calculation

Convert mol of given mass to mol of the mass that needs to be figured out from the balanced reaction.

Third step of mass to mass calculations

Convert the moles of the substance from step 2 to grams

What should you do with mass to mass calculations

Read the problem closely so you know what elements you are trying to find

When molarity is given in a question, what do you change to mass to mass formula?

Change the first step to the molarity formula:
(there is no molar ratio here usually)

What is the molarity formula:

Mol (of solution)

———————-

1000ml Soln (or 1 L)

What is % Yield Formula

% Yield = | experimental value | / accepted value (100)

What is % Error Formula

% Error = | accepted value - experimental value | / accepted value (100)

When explaining errors in labs you should NOT:

Explain the error with human error (I measured wrong, balance off, calculate something wrong)

Only say what you can directly support

When explaining labs you should:

Make observations during experiment and offer an explanation. For example the oxygen reacted with the aluminum overnight.

How to answer:

Mol of x element —> Mol of y element

How many moles of X element will form if moles of X element are used according to the reaction.

Multiply the given number by the molar ratio.

How to answer:

Mol of x element —> Grams of y element

Multiply by molar ratio then convert to grams

How to answer:

Grams of x element —> Grams of y element

Convert grams of x to moles

Convert moles of x to moles of y (molar ratio)
Convert moles of y to grams (molar mass *)

How to answer:

Volume of x element would x moles of element produce.

Multiply element by liters (22.4L)

How do you solve for a specific variable in a formula?

Rearrange the formula algebraically to isolate the variable you want, keeping units consistent.