Pre-Lab 19B: Acids, Bases and pH

Purpose

Life exists inside a certain range of pH values.

A pH value describes whether a solution is acidic, basic (alkaline), or neutral by describing the concentration of hydronium ions in a solution.

An acid is a substance that produces hydronium (H3O+) ions when dissolved in water,

and a base (or alkali) is a substance that produces hydroxide (OH-) ions when dissolved in water.

Neutral solutions have equal numbers of H3O+ and OH- ions.

• In this investigation, you will learn the pH of several common solutions by making a pH scale using a pH indicator and chemicals of known pH.

• You will also identify two ‘mystery’ chemicals (unknowns) with your created pH scale/table.

• You will be graded on lab performance and product accuracy/write-up

Key Question

• What is pH?

Background

• Define:– pH– Acid– Base

Drawing

• Draw figure 19.27 from your text book

Section1:

Make your pH predictions for the chemicals BEFORE EXPERIMENT!!!!

Section 2:

Work in pairs:

• To create your pH scale, you will be using solutions 1 to 7 in the table below.

• You will be using a 12 holed well plate, per row

• Number each of the wells, use pencil !!!!, to correlate to the number of each of the solutions on the data chart

• Number 4, red cabbage, is the control

• What is a control?

• Place 3 drops of the cabbage/control into the first 7 labeled wells

• Put pipettes back into the correct solutions

• What happens when the pipettes are wrongly placed?

Section 2B:

Finish the 5 remaining substances using the same procedure as we did in the initial 7 solutions

Use the first 7 solution findings to determine the last 5 solution pH’s

Wash well plates extremely thoroughly, why?

Stack well plates upside-down and perpendicular to each other

Post Lab: