Conclusion

You should finish your report with a short statement commenting on what was achieved, and what the final numerical result/s were. Think of it as a spoiler for your whole lab report! Your conclusion should answer all parts of your aim.

For example:

If the aim is: Determine the concentration of Vitamin C in a fruit juice via a redox titration against N-bromosuccinimide.

The conclusion might be: Berri orange juice (2000 μL aliquots, in triplicate) was titrated against a 0.104 M solution of N-bromosuccinimide. The concentration of Vitamin C in the fruit juice was determined to be 55.0 mg/L.

Glove Safety in the Lab

• Gloves are essential in the chemistry lab to protect against dangerous chemicals.
• They prevent immediate issues like chemical burns and long-term exposure risks.
• Along with enclosed shoes, lab coats, and safety glasses, proper glove use is critical.
• Knowing when to remove gloves is just as important as wearing them.
• To prevent cross-contamination, gloves should be removed immediately after completing a task (e.g., pouring an acid).
• Avoid touching common surfaces (e.g., drawer handles, notes, or your face) while wearing gloves.
• Remind classmates if they are wearing gloves inappropriately, as chemical transfer can pose a risk to everyone.

The graphic below highlights the many factors that gloves can protect against.

It also notes how many things you can unknowingly transfer chemicals onto if you aren't constantly aware of what you are doing.

Examine the graphic and answer the following questions.

 If you don't remove your gloves after you pour acid into a beaker, which of the following might be at risk of transfer contamination? Select the most correct answer.

When writing an aim, it should be in the format of the Goal (what do you want to achieve) and the Means (how you plan to achieve it).

Read over Exercise 3 in your lab manual to assist you with completing the aim for this experiment. Record the aim in your laboratory notebook, so that you will be able to address it when you write the conclusion for your lab report.

Aim:

To investigate and observe different chemical transformations of

Mole calculation

If you add 10.0 mL of 1.9 M NaOH, how many moles of NaOH would that be? You will need to calculate it using n = cv. Report your figure to two decimal places.

(If you are struggling with some of the maths in Chemistry there is a lot of help. See the maths hub on Moodle and talk to you TA or unit coordinator to find support.)

How can you know that during the practical session the amount of NaOH you will use to convert Cu²⁺ to Cu(OH)₂ will be in excess?

The Analytical Balance Room

• The room in the centre of the 1st Year laboratories houses our analytical balances.
• Analytical balances are highly sensitive and can measure masses to the microgram.
• To maintain their accuracy, the balances are serviced and calibrated annually.

Figure 1: Analytical balance

To ensure the analytical balances are kept in working order we must:

• Prevent solids or liquids from getting under the balance pan (to avoid corrosion and mechanical interference). Contamination under the pan can cause significant damage, costing thousands of dollars in repairs!!
• Ensure the electronics remain in good condition by never operating an analytical balance while wearing gloves.

From the list below, select the items that should not be worn or taken into the analytical balance room.

Interpreting atomic-scale depictions

Which of the following images best represents the structure of NaCl after dissolution?

Note that atomic radius has not been taken into account for the following images.

Balance the equation:

xCu²⁺_(aq) + yOH^-_(aq) → Cu(OH)_2(s)

x =

y = 

Determine the ratio between OH^- and Cu²⁺ for this equation:

Ratio (OH^-:Cu²⁺) = :

In chemistry, chemical equations are written to assist with explaining observations. Today you will be writing three forms of equations:

- full equations,

- ionic equations and,

- net ionic equations.

When writing equations always balance the equations and always include states i.e. whether your material is a liquid (l), gas (g), aqueous (aq) or solid (s). In most reports there are marks specifically for assigning the correct states and balancing the equation. 

Start the process by writing out the reactants on the left hand side (LHS) of the reaction arrow, and the products on the right hand side (RHS) (1). Next, balance the LHS and the RHS – there should be exactly the same number of each type of atom on both sides (2). Finally, add in the states (3) – use your observations to guide you if you are not sure.

Zn   +   HCl   ⇌   ZnCl₂   +   H₂                              (1) Here the LHS & RHS are not balanced

Zn   +   2 HCl   ⇌   ZnCl₂   +   H₂                            (2) Double the HCl on the LHS to balance the Cl & H atoms

Zn_(s) + 2 HCl_(aq)  ⇌  ZnCl_2(aq) + H_2(g)                  (3) Add in states and you have a full, balanced equation!

Notice that the HCl and ZnCl₂ are depicted as ‘aqueous’. When performing a reaction using water as the solvent, acids, bases and salts will usually be dissolved in the water, and will thus be present in their ionic (charged) forms. These ions (charged atoms or molecules) will not be bonded together when in solution, as they will be surrounded by water molecules. This can be represented by writing an ionic equation (4). The HCl and ZnCl₂ are now represented as dissociated ions:

Zn_(s) + 2 H⁺_(aq) + 2 Cl^-_(aq)  ⇌  Zn²⁺_(aq) + 2 Cl^-_(aq) + H_2(g)                   (4)

From the ionic equation we can now determine which atoms/ions have undergone a physical change, and which are just spectator ions. When writing the net ionic equation we omit the spectator ions, as they do not play a part in the actual chemical reaction. In this example, the chloride ions (Cl-) do not undergo a change in state (i.e. they remain aqueous) and are thus omitted from the net ionic equation (5):

Zn_(s) + 2 H⁺_(aq) ⇌  Zn²⁺_(aq) + H_2(g)                                                      (5)

Answer the following given the information above:

a.   Αg⁺_(aq) + 2 ΟΗ^-_(aq)                 ⇌         Ag₂O_(s) + Η₂Ο_(l)

b.  KOH_(aq) + HCl_(aq)            ⇌             KCl_(aq) + H₂O

c.  This equation has two spectator ions, one on the left hand side and one on the right hand side. Which are the spectator ions?

Cd_(s) + 2 H⁺_(aq) + 2 Cl^-_(aq)               ⇌             Cd²⁺_(aq) + 2 Cl^-_(aq) + H_2(g)  

Left hand side                                                    Right hand side

Calculate the number of moles, n, of CuCl₂.2H₂O in 0.12 g of copper (II) chloride dihydrate:

• Determine molecular mass, M, of CuCl₂.2H₂O (record your answer to 1 decimal place) g mol^-1 
• Determine the number of moles, n, in 0.12 g of CuCl₂.2H₂O

Record your answers in scientific notation (i.e. 6.1E-9) to two significant figures:  moles

(If you are struggling with some of the maths in Chemistry there is a lot of help. See the maths hub on Moodle, attend the Drop in sessions in the Chemistry Learning Centre, or talk to you TA or unit coordinator to find support.)