Introduction to pH LAB-AIDS pH Kit #80. pH Living things have certain pH ranges for normal biochemical processes to occur. pH is a logarithmic scale for.

Introduction to pH

LAB-AIDS pH Kit #80

pH

• Living things have certain pH ranges for normal biochemical processes to occur.

• pH is a logarithmic scale for measuring acids and bases video

• Measured through indicators or pH meter

Properties of Acids & Bases

• Acid – Taste tart or sour– Conduct electricity– Have more hydronium

ions

– H3O+

• Base (Alkaline) – Taste bitter – Feel slippery– Have more hydroxide

ions– OH-

–Buffers are chemicals that neutralize the effects of adding small amounts of either an acid or a base to a solution.

Strongest acid

Weak acid

Neutral

Weak Base

Strongest base

If “Normal rain water” is pH 6, then what would the pH of acid rain be?

SAFETY

• NO tasting, smelling, touching of liquids• NO tasting, smelling of papers• NO wandering – be aware while cleaning up.• Everyone wears goggles to protect eyes from

splashes• One person from team wears gloves while

handling materials• First Aid – wash affected area with plenty of

water.

CLEANUP

• Use toothpicks to remove pH paper. Throw toothpicks and pH paper in white barrel near sink

• Pour contents of Chemplate into the BEIGE water basin

• Dip the Chemplate into the GREEN bucket 5x

• Rinse Chemplate out in RUNNING water• Leave Chemplate on counter

Data Table

• Create a data table to account for:– Material tested (6 items)– Cavity number (#)– Original color– Color change for acid (HCl)– Color change for base (NaOH)

Lab Setup

• Setup the Chemplate as follows:• Phenol red: one drop in cavities 1 and 2• Phenolphthalein: one drop in cavities 5 and 6• Bromthymol Blue: one drop in cavities 9 and 10• Red litmus paper: ¼” square in cavities 3 & 4• Blue litmus paper: ¼” square in cavities 7 & 8• Universal pH Indicator paper: ¼” square in

cavities 11 & 12

Lab Procedure

• Add one drop of dilute Hydrochloric Acid (HCl) to cavities 1,5, and 9. Stir with toothpick.

• Add one drop of dilute Sodium Hydroxide (NaOH), a base to cavities 2,6, and 10. Stir with toothpick.

• Record data into table.• For paper strips in cavities 3 and 7 add one drop of HCl.

Record data into table.• For paper strips in cavities 4 and 8 add one drop of

NaOH. Record data into table.• Cavity 11 – 1 drop of HCl; Cavity 12 – 1 drop of NaOH.

Compare color to pH scale on vial.

Post Lab Questions

• How do you think litmus paper is made?• Of what value is Universal pH Indicator paper?• How do you think Universal pH Indicator paper is made?• A student pH tests several items and is asked to place

the results in order of strongest acid to weakest acid. What should the results look like? Values are 6.7, 7.0, 3.5, 4.2, 8.9, 2.0, and 13.

• Add to your notes – What color do acids turn blue litmus paper? Red litmus paper? What color do bases turn blue litmus paper? Red litmus paper?

Lab Materials

Before & After Photos

Chemplate after setup / prior to

procedure

Chemplate after procedure is

finished