Pharmaceutical Calculations Lab 2
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Questions and Answers

What is the unit of weight in the Imperial system that is equivalent to 16 ounces?

  • Troy ounce (oz t)
  • Grain (gr)
  • Drachm (ʒ)
  • Pound (lb) (correct)

What is the term used to describe the closeness of agreement among a set of results?

  • Sensitivity
  • Reliability
  • Precision (correct)
  • Accuracy

What is a common source of error in weight measurement?

  • Not cleaning the balance regularly
  • Using an electronic balance for rough weights
  • Failure in zeroing of the balance (correct)
  • Incorrect use of a watch glass

What is the primary purpose of using a watch glass when weighing solids?

<p>To contain the solid being weighed and prevent spillage (B)</p> Signup and view all the answers

Why should a balance be located in a well-lighted place?

<p>To reduce the risk of error due to poor visibility (B)</p> Signup and view all the answers

What is the weight in grams of 1 drachm?

<p>4 gm (C)</p> Signup and view all the answers

What is the formula to calculate the percentage error?

<p>(Measured value - Theoretical value) × 100 % (C)</p> Signup and view all the answers

What is the difference between systematic and random errors?

<p>Random errors arise from random fluctuations in the measurements (C)</p> Signup and view all the answers

What is the weight in kilograms of 1 pound?

<p>2.2 kg (B)</p> Signup and view all the answers

What is the unit of weight in the metric system that is equal to 0.065 grams?

<p>Grain (C)</p> Signup and view all the answers

Study Notes

Pharmaceutical Measurements

  • Weight is measured using a balance, which comes in different types:
    • Double beam balance for rough weights
    • Electronic balance for accurate and sensitive weights

Accuracy and Precision

  • Accuracy refers to the closeness of a measurement to the true value
  • Precision refers to the closeness of agreement among a set of results

Rules for Using and Caring for a Balance

  • Locate the balance in a well-lit, vibration-free area, away from dust, moisture, and corrosive vapors
  • Keep the balance clean at all times; remove any chemical spills immediately
  • Use a watch glass for weighing solids and a stoppered bottle for corrosive substances or liquids
  • Never place materials to be weighed directly on the pan
  • Check the balance's adjustment, including zeroing, before each weighing

Sources of Errors in Weight Measurement

  • Air currents
  • Failure to zero the balance
  • Incorrect posture of the balance (must be on a smooth surface)

Systems of Measuring Weight

  • Imperial system: units of weight include grain (gr), drachm (ʒ), ounce (oz), and pound (lb)
  • Metric system: units of weight include gram (g), kilogram (kg), and milligram (mg)

Relationships between Imperial and Metric Systems in Weight Measurement

  • 1 grain = 0.065g
  • 1 gm = 15.432 grains
  • 1 drachm = 4 gm
  • 1 ounce = 30 gm
  • 1 kg = 2.2 pounds

Bias (Systematic) and Random (Accidental) Errors

  • Bias errors are consistent and repeatable, while random errors arise from random fluctuations in measurements
  • To differentiate between the two: random errors are reduced when the experiment is repeated many times, while bias errors remain constant
  • Absolute error = measured value - theoretical value
  • Percent error = (measured value - theoretical value) × 100% / theoretical value

Example of Error Calculation

  • A prescription calls for 800mg of a substance, but the measured value is 850mg; the percentage of error is 6.25%

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Description

This quiz covers pharmaceutical measurements, weights, and balances, including types of balances and the difference between accuracy and precision.

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