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Worksheet Grade 9 Health & Consumer Science

The Yardley Home Water-Test Kit: pH, Chlorine, and Turbidity

Grade 9 consumer-health worksheet reading a fictional home test kit and comparing pH, chlorine, turbidity, and hardness to common water-quality guidelines.

Objectives

  1. Students will compare home water-test readings to common guideline ranges for pH, chlorine, and turbidity.
  2. Students will convert a hardness reading from grains per gallon to milligrams per liter.

Vocabulary

Turbidity
Turbidity is a measure of how cloudy or murky water looks because of tiny particles floating in it. Clear water has low turbidity, and muddy water has high turbidity.
Chlorine residual
Chlorine residual is the small amount of chlorine still left in the water after it leaves the treatment plant. It keeps protecting the water from germs all the way to your faucet.
pH
pH is a number that tells whether water is acidic, like lemon juice, or basic, like baking soda mixed in water. Pure water sits in the middle of the scale at a pH of 7.

Also: hardness

Teacher overview

Home water-test kits report several numbers at once, and reading them means knowing what each number should be. Common guidelines include a pH range of 6.5 to 8.5, a chlorine residual usually held between 0.2 and 2.0 mg/L with a maximum of 4.0 mg/L, and a treatment-plant standard of 0.3 NTU for the turbidity of filtered water. This worksheet has students read a fictional test from the Yardley household, compare each reading to its guideline, and convert a hardness result to a second unit. All readings come from the fictional figures given in the items.

The Yardley Home Water-Test Kit: pH, Chlorine, and Turbidity — Grade 9 Health & Consumer Science
Name: ____________________________ Date: ______________

Student Worksheet

Suppose the Yardley household ran a home test kit. The fictional readings were pH 7.4, chlorine residual 0.8 mg/L, turbidity 0.4 NTU, and hardness 7 grains per gallon. Use the guidelines stated in each item and show your work.

  1. The secondary standard range for drinking-water pH is 6.5 to 8.5. The kit read pH 7.4. Is that inside the range?
  2. Chlorine residual in distribution is usually 0.2 to 2.0 mg/L. The kit read 0.8 mg/L. Is that inside the usual range?
  3. The maximum residual disinfectant level for chlorine is 4.0 mg/L. How far below that maximum is the 0.8 mg/L reading?
  4. Treatment plants must keep filtered water at or below 0.3 NTU in 95 percent of monthly samples. The kit read 0.4 NTU. How many NTU above that plant standard is the reading?
  5. What percent of the 4.0 mg/L chlorine maximum is the 0.8 mg/L reading?
  6. The kit read hardness of 7 grains per gallon. Using 1 grain per gallon equals about 17.1 mg/L, convert 7 grains per gallon to mg/L. Round to the nearest whole number.
  7. The kit's chart labels water from 7 to 10.5 grains per gallon as "hard." Is the Yardley reading in the hard range?
  8. Which single reading is outside its recommended range or target?
  9. The middle of the pH range is 7.5. How far is the Yardley reading of 7.4 from that middle value?
  10. Based on all four readings, is the Yardley tap water broadly within common guidelines, and which result would you keep an eye on? Explain.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

The Yardley readings below are fictional figures built into the scenario.

  1. Answer: Yes. A pH of 7.4 falls between 6.5 and 8.5, so it is inside the range.
  2. Answer: Yes. A chlorine residual of 0.8 mg/L falls between 0.2 and 2.0 mg/L, so it is inside the usual range.
  3. Answer: 3.2 mg/L. The 4.0 mg/L maximum minus the 0.8 mg/L reading equals 3.2 mg/L below the maximum.
  4. Answer: 0.1 NTU. The 0.4 NTU reading minus the 0.3 NTU plant standard equals 0.1 NTU above the standard.
  5. Answer: 20 percent. 0.8 divided by 4.0 is 0.20, which is 20 percent of the maximum.
  6. Answer: 120 mg/L. 7 grains per gallon times 17.1 mg/L per grain equals 119.7, which rounds to 120 mg/L.
  7. Answer: Yes. A reading of 7 grains per gallon is at the low end of the 7 to 10.5 hard range, so it counts as hard.
  8. Answer: Turbidity. The 0.4 NTU turbidity reading is above the 0.3 NTU value, while the other three readings are within their guidelines. The 0.3 NTU value is a standard for water leaving the plant, not a limit for one tap sample, so this is not a violation, but it is the reading worth retesting.
  9. Answer: 0.1. The middle value is 7.5, and 7.5 minus 7.4 equals 0.1 below the middle of the range.
  10. Answer: Broadly within guidelines. Three of the four readings meet common ranges, and the turbidity of 0.4 NTU is the one slightly above its target, so it is the result to watch and possibly retest.

Differentiation

Support

Provide a one-page guideline card listing each range next to a blank box for the Yardley reading, so students line up the reading against its standard before answering. Allow calculators for items 3, 5, and 6.

Extension

Ask students to design a follow-up test plan: which reading should be retested first, how soon, and what a second high turbidity result might tell the household about its plumbing or its water source.

ELL supports

Pre-teach "turbidity," "residual," and "hardness" with a photo of clear versus cloudy water and a labeled test strip. Provide a sentence frame for item 8: "The reading outside its range is ___ because ___ is above the target of ___."