SI Units and Concentration Calculations

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Questions and Answers

What is the primary function of air displacement in the context of a centrifuge?

To maintain liquid contact with the piston

To use suction for sample aspiration (correct)

To ensure maximum capacity of liquid transfer

To heat the sample during operation

Which parameter is not typically checked to ensure quality control in air displacement methods?

Humidity (correct)

Temperature

Timer

Speed

How does a positive displacement method operate compared to air displacement?

It employs a complex electronic system

It draws liquid directly with the piston (correct)

It maintains an air gap during operation

It does not use a piston

What characteristic defines Type I reagent water compared to Types II and III?

Lower maximum contaminant levels Signup and view all the answers

Which component is essential in a positive displacement pipette system?

Disposable piston Signup and view all the answers

What is a primary characteristic of soft glass?

Low thermal resistance Signup and view all the answers

What is a disadvantage of flint glass?

Release of alkali causing errors Signup and view all the answers

What is a recommended use for low actinic glass?

Containing photosensitive substances Signup and view all the answers

Which type of glass is most commonly used for disposables?

Flint glass Signup and view all the answers

What effect does the piston in a pipette have during operation?

It displaces air to equal the volume of liquid aspired Signup and view all the answers

Which glass type provides high thermal resistance?

Silica glass Signup and view all the answers

Which characteristic makes soft glass different from flint glass?

Soft glass has low thermal resistance Signup and view all the answers

What type of sample is low actinic glass recommended for?

Viscous or high-density samples Signup and view all the answers

What is the molarity of a 1-liter solution containing 10 g of sodium hydroxide? (Molar mass of NaOH = 40 g/mol)

0.5 M Signup and view all the answers

What is the normality of a 1-liter solution containing 24.5 g of sulfuric acid (H2SO4)? (Molar mass = 98 g/mol)

2 N Signup and view all the answers

What is the molarity of a 3 M sulfuric acid solution?

3 N Signup and view all the answers

What is the molality of a solution containing 50 g of NaCl dissolved in 1 kg of water? (Molar mass of NaCl = 58.44 g/mol)

0.86 m Signup and view all the answers

How many milliliters of 70% ethanol are needed to prepare 35 mL of a 40% solution?

40 mL Signup and view all the answers

What is the prefix for 10^-12 in SI units?

pico Signup and view all the answers

What is the significance of glycosylated hemoglobin (HbA1c) in monitoring blood glucose levels?

It provides an index of average blood glucose levels over the past 2-3 months. Signup and view all the answers

What is the equivalent mass of sulfuric acid (H2SO4) if its normality is 2 N in a 1-liter solution?

98 g Signup and view all the answers

Which of the following conditions can affect the reliability of HbA1c measurements?

Hemolytic disorders Signup and view all the answers

Which of the following prefixes represents a factor of 10^3?

kilo Signup and view all the answers

Which method is commonly used for estimating HbA1c in laboratory settings?

Chromatography Signup and view all the answers

What glucose concentration does a 1-hour post-glucose load indicate when it exceeds 180 mg/dL?

Diabetes mellitus Signup and view all the answers

How are glucose levels measured in the Dubowski reaction?

By assessing the intensity of color reaction Signup and view all the answers

What is the significance of a 2-hour post-load glucose test?

It confirms the diagnosis of diabetes mellitus. Signup and view all the answers

Which of the following is NOT a symptom indicative of diabetes mellitus?

Hypertension Signup and view all the answers

What does the reduction of cupric ions to cuprous ions in the copper reduction test indicate?

The presence of glucose in a sample. Signup and view all the answers

Which method utilizes a color change from yellow-orange to colorless to indicate glucose presence?

Nelson Somogyi method Signup and view all the answers

What is required for a diagnosis of gestational diabetes during an OGTT?

Two or more glucose levels meeting specific criteria. Signup and view all the answers

Which statement accurately describes the condition of falsely increased results in copper reduction tests?

Falsely increased results can occur with other reducing substances present. Signup and view all the answers

What does a measurement of 200 mg/dL signify in the context of glucose testing?

It confirms a diagnosis of diabetes mellitus. Signup and view all the answers

What is the preferred test to confirm a diagnosis when the standard load for glucose is involved?

2-hour post-load glucose test. Signup and view all the answers

Study Notes

SI Units and Prefixes

Time - 1 minute = 60 seconds
Liter - 1 liter = 1 cubic decimeter (dm³) = 10⁻³ cubic meters (m³)
Angstrom - 1 Angstrom = 0.1 nanometer (nm) = 10⁻¹⁰ meters (m)
Prefixes - A system for denoting multiples and submultiples of SI units using specific symbols:
- atto (a) - 10⁻¹⁸
- femto (f) - 10⁻¹⁵
- pico (p) - 10⁻¹²
- nano (n) - 10⁻⁹
- micro (µ) - 10⁻⁶
- milli (m) - 10⁻³
- centi (c) - 10⁻²
- deci (d) - 10⁻¹
- deka (da) - 10¹
- hecto (h) - 10²
- kilo (k) - 10³
- mega (M) - 10⁶
- giga (G) - 10⁹
- tera (T) - 10¹²
- peta (P) - 10¹⁵
- exa (E) - 10¹⁸

Concentration Calculations

Molarity - moles of solute per liter of solution
Normality - grams of solute per gram molecular weight × liter of solution
Example 1: A 1-liter solution containing 10g of sodium hydroxide (NaOH)
- Molar mass of NaOH = 40 g/mol
- Molarity = 10 g / (40 g/mol × 1 L) = 0.25 M
Example 2: A 1-liter solution containing 24.5 g of sulfuric acid (H₂SO₄)
- Molar mass of H₂SO₄ = 98 g/mol
- Molarity = 24.5 g / (98 g/mol × 1 L) = 0.25 M
- Normality = 2 × 0.25 M = 0.5 N (sulfuric acid has two acidic hydrogen atoms)
Example 3: Calculating molarity from normality - 0.3N H₃PO₄
- Phosphoric acid (H₃PO₄) has three acidic hydrogen atoms.
- Molarity = 0.3N / 3 = 0.1 M
Example 4: Calculating normality from molarity - 3M sulfuric acid
- Normality = 2 × 3 M = 6N (sulfuric acid has two acidic hydrogen atoms)

Expressions of Concentration

Molarity - Measures the number of moles of solute per liter of solution.
Molality - Measures the number of moles of solute per kilogram of solvent.

Ethanol Dilution

Example: How many milliliters of 70% ethanol are needed to prepare 35 mL of 40% ethanol?
- Using the formula: V₁C₁ = V₂C₂
- V₁ = ? (Volume of 70% ethanol)
- C₁ = 70%
- V₂ = 35 mL (Final volume)
- C₂ = 40%
- V₁ = (V₂C₂) / C₁ = (35 mL × 40%) / 70% = 20 mL
Therefore, 20 mL of 70% ethanol are needed.

Glassware: Types and Characteristics

Soft Glass (Boron-free glass)
- Low thermal resistance (can't be heated)
- Used for strong acids and alkalis
Flint Glass (Soda lime glass)
- Most inexpensive, commonly used for disposables
- Made from silicon, calcium, and sodium oxides
- Releases alkali, which can cause errors in some measurements
Low Actinic Glass (Amber-colored/coated glass)
- Reduces light transmission
- Used for photosensitive substances

Pipettes: Air Displacement vs. Positive Displacement

Air Displacement Pipette:*
Uses suction to draw sample into a disposable polypropylene tip.
Piston does not come in contact with liquid (air gap).
Positive Displacement Pipette:*
Operates like a hypodermic syringe.
Piston is in direct contact with the liquid being aspirated.
Tips are reusable, but must be rinsed out.
Components: disposable piston, disposable capillary (glass or Teflon), piston seal.

Reagents and Reagent Water

Copper Reduction Method (for glucose measurement)
- Based on Benedict's principle: cupric ions are reduced to cuprous ions by glucose in the presence of heat and alkaline environment.
- Cuprous ions are oxidized by PMA, AMA.
- Other reducing agents can falsely increase glucose levels.
- Examples: Foilin-Wu (colorimetric, blue), Nelson Somogyi (colorimetric, blue), Ferricyanide (yellow orange, becomes colorless when reduced).
Condensation Method (for glucose measurement)
- Dubowski reaction: intensity of color reaction is proportional to glucose concentration (colorimetric, green)
- Reaction of glucose with aromatic amines (ortho-toluidine).
Types of Reagent Water
- Type I - Most pure, used for critical analysis.
- Type II - Less pure than Type I, used for general laboratory work.
- Type III - Least pure, used for rinsing glassware.

Glycemic Control Measures

Glycosylated Hemoglobin (HbA1c)
- Hb A with glucose irreversibly attached to one or both N-terminal valines of the β-chains.
- Provides an index of average blood glucose levels over the past 2-3 months (lifespan of RBCs).
- Unreliable in patients with hemolytic disorders and hemoglobinopathies (shortened RBC lifespan).
- Sample: hemolysate (from EDTA whole blood).
- Methods: Electrophoresis, chromatography, immunoassays.

Enzymatic Methods

Used for glucose measurement.
Highly sensitive and specific.

Lipids and Lipoproteins

Not covered in the provided text.

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Description

This quiz covers essential concepts related to SI units and their prefixes, as well as concentration calculations such as molarity and normality. It provides examples and definitions to enhance understanding of these fundamental topics in chemistry.