Titrations

Titration is an experimental technique used to determine the concentration of an unknown solution.

•  buret - contains the known solution, used to measure  how much is added
• stopcock(tap) - valve used to control the flow of solution from the buret
• pipet - used to accurately measure the volume of a unknown solution
• erlenmeyer flask - container for unknown solution
• indicator - used to identify the end point of the titration
• stock solution - known solution

Janine R

Solution Stoichemetry Question Examples

A beaker contains 100mL or 1.5M HCl. Excess zinc is added to the beaker. Determine how many litres@STP of hydrogen gas should be produced.


2HCl + Zn --> ZnCl2 + H2

1.5mol x 0.100L x 1 x 22.4L = 1.7L
     L                       2     mol

Determine the number of mles of H2O produced when 0.250L of 0.100M NaOH is neutralized by H2SO4.


2NaOH +H2SO4 --> Na2SO4 + 2H2O


0.100mol x 0.250L x 2 = 0.025mol
      L                          2





Janine R

Solution Stoichimetry

Solutions: homogenous mixtures composed of a solute and a slovent
-- solute : chemical present in the lesser amount
                             (whatever is dissolved)
--solvent : chemical present in the greater amount
                            (whatever does the dissolving)

- chemicals that dissolved in water are aqueous


MOLARITY

-concentrations can be expressed in many difderent ways
     --> g/L , mL/L, % by volume, % by mass, mol/L
- most common one we will be doing is mol/L

watch this video to learn how to do molarity practice problems and learn the molarity volume

http://www.youtube.com/watch?v=Ed1S0fLBqk4

Nicole H

TEST NEXT CLASS !

We will be having a test next class on the following conversions:

mole--->mole  given mole x need = resultant mole
                                             have

mole--->mass  given mole x need x mm = resultant mass
                                             have   1mol

mass--->mole  given mass x 1mole x need = resultant mole
                                              mm       have

mass--->mass  given mass x 1mole x need x mm = resultant mass
                                               mm      have   1mol



Janine R

Limiting Reactants

In chemical reactions, usually one chemical gets used up before the other. The chemical used up first is the limiting reactant. Once the limiting reactant is used up the reaction is stopped.
- Limitng reactant determines the quantity of products formed
- to find the L.R. assume one reactant is used up. Determine how much of this reactant is required.

Example :

2 H2 + O2 --> 2 H2O
8 mol x 2  = 16 mol
            1
Hydrogen = limiting factors

please watch this video for more examples of limiting reactants.. thanks :)
http://www.youtube.com/watch?v=fQyS7cZIJ1Q

Nicole H

Energy and Percent Yield

• enthalpy is the energy stored in chemical bonds
• symbol of enthalpy is H
• unit of Joules is J
• change in enthalpy is delta H
• in exothermic reactions enthalpy increases
• in endothermic reaction enthalpy increases

Calorimetry:

-to experimentally determine the heat released we need to know 3 things

1. temperature change deltaT

2. Mass. (m)

3. specific heat capacity (C) --> ability to hold heat

equation: H = mCT

Example:

- Calculate the heat required to warm a cup of 400g of water (c=4.8J/g celsius) from 20 to 50 degrees

H= mCT

H= (4.oo)(4.18)(30)

H= 50160 J --> 50.2 kJ

PERCENT YIELD

• the theoretical yield of a reaction is the amount of products that should be form
• the actual amount depends on the experiment
• the percent yiels is like a measure of success

- how close is the actual amount to the predicted amount?

    %yield = actual              x 100

                   theoretical

Nicole H

Other Conversions

• Volume at STP can be found using hte conversion factor 22.4L/mol
• Heat can be included as a seperate term in chemical reaction called enthalpy
• reaction that releases heat are exothermic
• reaction that absorbs heat are endothermic
• both can be used in stoichiometry

Examples:

- if 5.og of potassium chlorate decompose according to the reaction below, what volume of oxygen gas @STP is produced?
                                                          2 KClO3 --> 2 KCl + O2
5.0g x 1mol x 3  = 0.0612 mol x 22.4L =  1.4 L
          120.6   2                           1 mol

-When zinc reacts with hydrochloric acid exactly 1.00 L of hydrogen gas is produced at STP what mass of zinc was reacted?
                                   Zn + 2 HCl --> H2 + ZnCl2
1.00 L x 1 mol x 1 x 65.4  = 2.92 g
              22.4L   1    1mol

Nicole H

Stoichiometry Investigation

Problem : Does stoichemistry accuratley predict the mass of products produced in chemical reaction?

In this experiment we have to figure out how many moles of percipitate were formed when 2.00g of Stronium nitrate is disslved in 50mL of water and then reacted with the excess copper sulphate.

1) carefully measure about 3.oog of copper(ii) sulphate.
2) crush the copper(ii) sulphae into a fine powder using a mortar and pestle.
3) dissolve the copper sulphate in 50 mL
4) measure 2.00g of stronium nitrate and sissolvr iy on 50 mL of watter
5) slowly pour the two solutions
6) stir the mixture to complete the reaction
7) write your group name on  a piece of filter paper
8) find and record the mass of the filter paper
9)using a funnel and a n erlenmeyer flask, place the filter paper in funnel. Slowly pur the mixture into the funnel
10) pour the filtrate into the waste colection bottle
11) place the filter paper in the drying oven and record the mass when its dry

After following the procedure we discoved the formed moles of percipitate was 0.00953 mol

Nicole H