UNIT 5.1

Laboratory Fundamentals & Solution Chemistry

Safety, glassware, and the math of the lab

🎯 After this unit, you will be able to:

Identify essential lab safety equipment and practices
Select appropriate glassware for different tasks
Calculate concentrations using molarity, percent solutions, and dilutions
Prepare buffers and understand pH

🧪 Welcome to the Biochemistry Lab

The biochemistry laboratory is where theory meets practice. Understanding fundamental lab skills—safety, solution preparation, and measurement—is essential for anyone working with plant samples. This unit will prepare you for the practical techniques covered in subsequent units .

Key insight: Accurate and reproducible results depend on proper technique. A small error in solution preparation can lead to completely misleading data. Take the time to master these fundamentals .

⚠️ Part 1: Laboratory Safety

Safety is the first priority in any laboratory. Understanding hazards and proper procedures protects you and those around you .

Personal Protective Equipment (PPE)

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Lab Coat

Protects skin and clothing from spills

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Safety Goggles

Protects eyes from splashes and fumes

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Gloves

Protects hands from chemicals

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Closed-toe Shoes

Protects feet from spills and broken glass

General Safety Rules

No food or drink in the laboratory
Know the location of safety equipment: eyewash station, safety shower, fire extinguisher, first aid kit
Never work alone in the lab
Label everything—contents, concentration, date, your initials
Dispose of waste properly—follow instructions for chemical, biological, and sharps waste
Report all accidents immediately, no matter how minor

Safety Data Sheets (SDS)

Every chemical has a Safety Data Sheet that provides critical information:

Hazards (flammability, toxicity, reactivity)
First aid measures
Handling and storage requirements
Spill cleanup procedures

📋 Did you know? SDS sheets are legally required to be readily available in any laboratory. They follow a standardized 16-section format, so once you learn how to read one, you can read them all .

🧴 Part 2: Laboratory Glassware and Equipment

Different types of glassware are designed for different purposes. Using the right glassware ensures accurate measurements .

Volumetric Glassware (for accuracy)

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Volumetric Flask

For preparing precise solutions

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Volumetric Pipette

For transferring precise volumes

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Volumetric Cylinder

For measuring approximate volumes

Other Common Glassware

Glassware	Use	Accuracy
Beaker	Mixing, heating, approximate volumes	Low (±5%)
Erlenmeyer flask	Mixing, titration, culturing	Low (±5%)
Graduated cylinder	Measuring approximate volumes	Medium (±1%)
Volumetric flask	Preparing exact solutions	High (±0.1%)
Volumetric pipette	Transferring exact volumes	High (±0.1%)
Micropipette	Small volumes (μL)	High (if calibrated)

🧪 [Diagram: Common laboratory glassware with labels — to be inserted]

🔬 Did you know? Volumetric glassware is calibrated "to contain" (TC) or "to deliver" (TD). Volumetric flasks are TC—they contain the stated volume when filled to the mark. Pipettes are TD—they deliver the stated volume when emptied properly .

⚗️ Part 3: Solutions and Concentrations

Solutions are homogeneous mixtures of a solute (what you're dissolving) in a solvent (usually water). Accurate concentration calculations are essential .

Molarity (M)

Molarity is moles of solute per liter of solution.

Molarity (M) = moles of solute / liters of solution

Example: To prepare 1 L of 1 M NaCl:

Molecular weight of NaCl = 58.44 g/mol
Mass needed = 1 mol × 58.44 g/mol = 58.44 g
Dissolve 58.44 g NaCl in water, bring to 1 L in volumetric flask

Percent Solutions

Type	Definition	Example
% w/v (weight/volume)	grams solute per 100 mL solution	5% NaCl = 5 g NaCl in 100 mL solution
% v/v (volume/volume)	mL solute per 100 mL solution	70% ethanol = 70 mL ethanol + 30 mL water
% w/w (weight/weight)	grams solute per 100 g solution	Less common in plant biochemistry

Example: To prepare 250 mL of 10% (w/v) sucrose:

10% means 10 g per 100 mL
For 250 mL: (10 g × 250/100) = 25 g sucrose
Dissolve 25 g sucrose in water, bring to 250 mL

Dilutions

The dilution equation: C₁V₁ = C₂V₂

Where C₁ = initial concentration, V₁ = volume of stock to use, C₂ = final concentration, V₂ = final volume .

Example: Prepare 100 mL of 0.1 M NaCl from 1 M stock:

C₁ = 1 M, V₁ = ?, C₂ = 0.1 M, V₂ = 100 mL
1 M × V₁ = 0.1 M × 100 mL
V₁ = (0.1 × 100) / 1 = 10 mL
Take 10 mL of 1 M stock, add water to 100 mL

Serial Dilutions

Serial dilutions are stepwise dilutions used to create a range of concentrations. Each step dilutes the previous solution by a constant factor (often 10-fold) .

🔢 [Diagram: Serial dilution showing 1:10 dilutions — to be inserted]

🧪 Serial Dilution for Standard Curve

To create a standard curve for protein assay, you might prepare BSA standards at 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 mg/mL. A serial dilution approach:

Prepare 1.0 mg/mL stock
Dilute 1:2 → 0.5 mg/mL
Dilute 0.5:2 → 0.25 mg/mL
Continue to create desired concentrations

This ensures accuracy and consistency across standards .

🧪 Part 4: Buffers and pH

pH is a measure of hydrogen ion concentration: pH = -log[H⁺]. Most biochemical reactions are pH-sensitive and require buffered solutions .

What is a Buffer?

A buffer is a solution that resists changes in pH when small amounts of acid or base are added. Buffers consist of a weak acid and its conjugate base (or weak base and conjugate acid) .

The Henderson-Hasselbalch Equation

pH = pKa + log([A⁻]/[HA])

Where pKa is the acid dissociation constant, [A⁻] is concentration of conjugate base, [HA] is concentration of weak acid .

Common Buffers in Plant Biochemistry

Buffer	pKa	Useful pH range	Common applications
Phosphate	7.2	6.2-8.2	General purpose, enzyme assays
Tris	8.1	7.1-9.1	Protein work, electrophoresis
MES	6.1	5.1-7.1	Plant cell culture, enzyme assays
HEPES	7.5	6.5-8.5	Cell culture, enzyme assays
Acetate	4.76	3.8-5.8	Extraction, chromatography

Preparing a Buffer

Example: Prepare 1 L of 0.1 M phosphate buffer, pH 7.2 (pKa = 7.2):

At pH = pKa, [A⁻]/[HA] = 1, so [HA] = [A⁻] = 0.05 M each
Use sodium phosphate monobasic (NaH₂PO₄, MW = 120) and dibasic (Na₂HPO₄, MW = 142)
Weigh 0.05 mol × 120 = 6.0 g NaH₂PO₄ and 0.05 mol × 142 = 7.1 g Na₂HPO₄
Dissolve in ~800 mL water, adjust pH with acid/base if needed, bring to 1 L

📊 Did you know? Buffers work best within ±1 pH unit of their pKa. Always choose a buffer with pKa close to your desired pH .

📓 Part 5: Keeping a Laboratory Notebook

A proper lab notebook is a legal record of your work. It should be:

Bound (not loose-leaf)
Numbered pages
Written in pen
Dated for every entry
Signed and witnessed for important entries

What to Include

Date and experiment title
Objective/hypothesis
Detailed protocol (or reference to protocol)
All data, including calculations
Observations (color changes, unexpected events)
Conclusions and next steps

Golden rule: If it's not written down, it didn't happen. Record everything immediately, never from memory .

✏️ Practice Problems

1. Molarity calculation: How many grams of glucose (MW = 180 g/mol) are needed to prepare 500 mL of 0.2 M glucose solution?

Show solution

moles = M × L = 0.2 × 0.5 = 0.1 mol
mass = 0.1 mol × 180 g/mol = 18 g glucose

2. Percent solution: How would you prepare 250 mL of 15% (w/v) sucrose?

Show solution

15% = 15 g per 100 mL
For 250 mL: (15 g × 250/100) = 37.5 g sucrose
Dissolve 37.5 g sucrose in water, bring to 250 mL

3. Dilution: You have a 5 M NaCl stock. How do you prepare 100 mL of 0.15 M NaCl?

Show solution

C₁V₁ = C₂V₂
5 × V₁ = 0.15 × 100
V₁ = (0.15 × 100)/5 = 3 mL
Take 3 mL of 5 M stock, add water to 100 mL

🇪🇹 Laboratory Practice in Ethiopia

Many Ethiopian universities and research institutions have biochemistry labs with varying levels of equipment. Key considerations:

Water quality: Distilled or deionized water is essential. If not available, proper distillation or deionization systems are needed.
Glassware washing: Proper cleaning (acid washes, detergent, multiple rinses) is critical for accurate results.
Reagent grade chemicals: Always use analytical grade chemicals when available.
Calibration: Pipettes, pH meters, and balances need regular calibration.

🧪 Low-Cost Alternatives

When resources are limited, improvisation may be necessary. For example:

Handmade pH indicators from local plants (red cabbage) for approximate pH
Simple distillation units for water purification
Gravimetric measurements using analytical balances (most critical)

However, safety should never be compromised .

📌 Unit Summary

Topic	Key points
Safety	PPE (lab coat, goggles, gloves), know safety equipment, never work alone, SDS sheets
Glassware	Volumetric for accuracy, graduated for approximations, TC vs. TD calibration
Molarity	M = moles/L; use MW to convert mass to moles
Percent solutions	% w/v = g/100 mL; % v/v = mL/100 mL
Dilutions	C₁V₁ = C₂V₂; serial dilutions for standard curves
Buffers	Resist pH change; choose pKa near desired pH; Henderson-Hasselbalch equation

Reflection question: You need to prepare 500 mL of 0.1 M phosphate buffer, pH 7.0. The pKa of phosphate is 7.2. Using the Henderson-Hasselbalch equation, calculate the ratio of [A⁻]/[HA] needed. What masses of NaH₂PO₄ (MW=120) and Na₂HPO₄ (MW=142) would you use?

📌 Key terms introduced

PPE SDS (Safety Data Sheet) Volumetric flask Molarity % w/v % v/v C₁V₁ = C₂V₂ Serial dilution pH Buffer pKa Henderson-Hasselbalch

✅ Check your understanding

What four items of PPE should you always wear in a biochemistry lab?
Why should you use a volumetric flask rather than a beaker to prepare a standard solution?
How many grams of NaCl (MW=58.44) are needed to prepare 250 mL of 0.5 M NaCl?
You have a 10 mg/mL BSA stock. How would you prepare 1 mL of 2 mg/mL BSA?
What buffer would you choose for an enzyme with optimal pH 6.5? Why?

Discuss your answers in the course forum.

Plant Biochemistry for Horticulture · HORT 202 · Dilla University · Last updated March 2026