You place a piece of paper on a balance and find that its mass is 0.63 g. You add a lump of NaOH to the paper and get a mass of 22.21 g. You remember that you forgot to tare the balance before taking this measurement. You tare the balance, add another lump of NaOH, and read 20.64 g. You add another lump of NaOH and read 38.98 g. How Much NaOH do you have on the balance, in grams, milligrams, micrograms and kilograms?

22.21 = mass paper + first lump NaOH

-0.63 = mass paper
-------------
21.58 = mass NaOH
Now you tare the 22.21 (paper+NaOH) to zero.
The second lump adds 20.64 the third lump + second lump = 38.98
So total NaOH = 38.98 + mass first lump of 21.58 for total of 38.98+21.58 grams. You convert to the other units.

By the way, the person making the problem should have used some material other than NaOH since solid NaOH absorbs CO2 and H2O from the atmosphere and besides corroding the balance pans will continually add moisture and CO2 from the air and will not have a stable weight.

To determine the amount of NaOH on the balance, we need to calculate the mass difference between each measurement.

1. Initial measurement:
Paper mass = 0.63 g

2. Second measurement:
Mass of paper + NaOH = 22.21 g
NaOH mass = (Mass of paper + NaOH) - Paper mass = 22.21 g - 0.63 g = 21.58 g

3. Third measurement:
Mass of paper + NaOH = 20.64 g
NaOH mass = (Mass of paper + NaOH) - Paper mass = 20.64 g - 0.63 g = 20.01 g

4. Fourth measurement:
Mass of paper + NaOH = 38.98 g
NaOH mass = (Mass of paper + NaOH) - Paper mass = 38.98 g - 0.63 g = 38.35 g

Therefore, the amount of NaOH on the balance is:
- In grams: 38.35 g
- In milligrams (mg): 38.35 g × 1000 = 38350 mg
- In micrograms (μg): 38.35 g × 1,000,000 = 38350000 μg
- In kilograms (kg): 38.35 g ÷ 1000 = 0.03835 kg

To find the amount of NaOH on the balance, we need to subtract the mass of the paper from each measurement.

1. Calculate the mass of NaOH in grams:
- Measurement 1: 22.21 g - 0.63 g (mass of the paper) = 21.58 g NaOH
- Measurement 2: 20.64 g - 0.63 g = 20.01 g NaOH
- Measurement 3: 38.98 g - 0.63 g = 38.35 g NaOH

2. Convert grams to milligrams:
- 21.58 g NaOH = 21.58 * 1000 mg = 21580 mg NaOH
- 20.01 g NaOH = 20.01 * 1000 mg = 20010 mg NaOH
- 38.35 g NaOH = 38.35 * 1000 mg = 38350 mg NaOH

3. Convert grams to micrograms:
- 21.58 g NaOH = 21.58 * 1,000,000 μg = 21580000 μg NaOH
- 20.01 g NaOH = 20.01 * 1,000,000 μg = 20010000 μg NaOH
- 38.35 g NaOH = 38.35 * 1,000,000 μg = 38350000 μg NaOH

4. Convert grams to kilograms:
- 21.58 g NaOH = 21.58 / 1000 kg = 0.02158 kg NaOH
- 20.01 g NaOH = 20.01 / 1000 kg = 0.02001 kg NaOH
- 38.35 g NaOH = 38.35 / 1000 kg = 0.03835 kg NaOH

So, the amount of NaOH on the balance is:
- 21.58 g, 21580 mg, 21580000 μg, or 0.02158 kg
- 20.01 g, 20010 mg, 20010000 μg, or 0.02001 kg
- 38.35 g, 38350 mg, 38350000 μg, or 0.03835 kg