كيف يحسب الرقم الهيدروجيني pH للمحاليل؟ How to calculate pH and pOH?

يحسب الرقم الهيدروجيني بالعلاقة: pH = -log[H⁺]، وللمحاليل المائية عند 25°C: pH + pOH = 14. إذا كان pH 7 فالمحلول قاعدي. [الصيغة الرمزية الموزونة: pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴]

1.2Unit 1: Lifestyle, Transport, Genes and Health

SNAB Diet & Health — IAL Edexcel Linear Revision Notes & Topical Questions

10 min read 14 parts Lesson 3 of 29 2 quizzes

📚 IAL Edexcel Linear Hub / Topical Revision

Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution

pH = -log[H⁺]  |  pOH = -log[OH⁻]  |  pH + pOH = 14  |  [H⁺][OH⁻] = 10⁻¹⁴

Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14

Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.

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Lesson summary

1.2 Diet and Health — IAL EDEXCEL LINEAR notes: Describe cardiovascular disease and its risk factors, evaluate risk data and treatments, and explain energy budgets, carbohydrates, lipids and the vitamin C practical.Cardiovascular disease (CVD) = conditions affecting the heart and…

Interaction of factors
Correlation and causation
Describing data
Drawing conclusions
Validity of data
Conflicting evidence

Part 1 of 12Cardiovascular disease and risk factors

1Cardiovascular disease (CVD)

Cardiovascular disease (CVD) conditions affecting the heart and blood vessels, usually associated with atherosclerosis and thrombosis.

2Risk factor

Risk factor a factor linked to an increased chance of disease, which does not guarantee the disease will occur.

Lifestyle factors include diet, smoking, alcohol intake and exercise, which are partly under individual control.
Environmental factors include air pollution and asbestos.
Genetic predisposition, age and biological sex are outside individual control.

3Interaction of factors

Interaction of factors many diseases result from several factors acting together, for example a high-cholesterol diet, inactivity and smoking all damage arteries.

4Correlation and causation

Correlation and causation a correlation between a risk factor and a disease does not always mean one causes the other.
Healthy choices are easier for some people than others because unhealthy food is often cheaper and exercise needs time.

Part 2 of 12Interpreting data and evaluating studies

Describing data

Describing data state the trend and quote numbers from the data.

Drawing conclusions

Drawing conclusions state only what the data show, as an association or correlation.
A causal relationship cannot be concluded from one data set.
Results cannot be extrapolated beyond the age group, species or setting studied.

Validity of data

Validity of data results are valid if they measure what they set out to measure and are analysed correctly.
Larger and random samples are more representative and reduce bias.
A control group gives a point of comparison, and all other variables should be controlled.
Statistical tests show whether differences are significant, and overlapping standard deviations mean the difference is not significant.
Repeats within a study and reproduction of the whole investigation show reliability.
Researchers should be unbiased, for example not paid to find a given result.

Conflicting evidence

Conflicting evidence one study is not enough, so similar studies are combined in a meta-analysis.
Conflicting evidence shows a different pattern from other studies and often signals other variables.

Part 3 of 12Perception of risk

Risk

Risk the chance or probability that a harmful event will occur, which should be supported by scientific evidence.

Overestimated risk

Overestimated risk it results from misleading media information, overexposure to information, personal experience, unfamiliarity with the event or severe harm.

Underestimated risk

Underestimated risk it results from lack of information, misunderstanding of risk factors, lack of personal experience, unfamiliarity or harm that is not immediate.

Part 4 of 12Treatments for CVD

Drug type	How it works	Effect on CVD risk
Antihypertensives	Lower blood pressure (hypertension)	Reduce endothelial damage, so fewer atheromas and thromboses
Statins	Block a liver enzyme needed to make cholesterol	Lower LDL concentration, so less atheroma formation
Anticoagulants	Reduce blood clotting (coagulation)	Lower the chance of thrombosis and blocked vessels
Platelet inhibitors (aspirin)	Prevent platelets clumping together	Prevent clot formation

Treatments for CVD

Antihypertensive types

Antihypertensive types beta blockers prevent increases in heart rate, vasodilators widen vessels and diuretics reduce blood volume by decreasing sodium and water reabsorption in the kidneys.

Risks

Risks each drug has side effects, so benefits are weighed against risks, for example excessive bleeding with anticoagulants and aspirin.

Part 5 of 12Energy budgets and diet

Energy budget

Energy budget energy input minus energy output.

Energy is released by respiration from carbohydrates and lipids in food.
Output includes growth, movement, reproduction and respiration.

Units

Calories equal kilocalories (kcal), and kilojoules (kJ) are the alternative unit.
An average adult needs about 2000 kcal or 8700 kJ per day.

Positive budget

Positive budget energy intake above output is converted to fat, giving weight gain and eventually obesity.

Negative budget

Negative budget intake below output uses fat reserves, giving weight loss and possibly underweight.

Complexity

Complexity not all calories are equal because the body processes fats, sucrose and fructose differently.

Part 6 of 12Monosaccharides and the glycosidic bond

Carbon compounds

Carbon compounds carbon forms stable covalent bonds in chains, branches and rings, so small monomers join into polymers by polymerisation.

Monosaccharide

Monosaccharide a simple sugar monomer containing C, H and O: triose (3C), pentose (5C, e.g. ribose) or hexose (6C, e.g. glucose).

Glucose has carbons 1–5 in a ring with carbon 6 above the ring.
Alpha glucose has H above and OH below carbon 1; beta glucose has H below and OH above.
Monosaccharides are soluble and store energy in many covalent bonds that are released in respiration.

Glycosidic bond

Glycosidic bond covalent bond formed when two hydroxyl groups on different monosaccharides react, releasing water.

Its name depends on the carbons involved, for example 1,4 or 1,6.
It forms by condensation and is broken by hydrolysis (adding water), as in digestion and glycogen breakdown.

Part 7 of 12Disaccharides and polysaccharides

Carbohydrate	Made from	Bond and structure	Role
Maltose	Glucose + glucose	1,4 glycosidic	Quick-release energy
Sucrose	Glucose + fructose	1,2 glycosidic	Quick-release energy (table sugar)
Lactose	Glucose + galactose	1,4 glycosidic	Quick-release energy
Amylose	Alpha-glucose	1,4 bonds, unbranched helix	Compact store in plants
Amylopectin	Alpha-glucose	1,4 and 1,6 bonds, branched	Store in plants with many ends for fast hydrolysis
Glycogen	Alpha-glucose	1,4 and 1,6 bonds, more branched than amylopectin	Store in animals and fungi

Disaccharides

Disaccharides they are soluble, sweet and easily broken to monosaccharides by digestive enzymes.

Storage polysaccharides

Storage polysaccharides starch and glycogen are compact and insoluble, so they have no osmotic effect on cells.
Starch is stored as granules in plastids such as amyloplasts.
Branching creates many terminal glucose molecules, so glucose is added or removed quickly.
Liver and muscle cells hold glycogen granules to support a high respiration rate.

Part 8 of 12Lipids and ester bonds

Lipids

Lipids they contain C, H and O with proportionally less oxygen than carbohydrates and are non-polar and hydrophobic.
Roles include energy yield and storage, insulation, buoyancy, protection and hormonal communication.

Triglyceride

Triglyceride glycerol joined to three fatty acids.

Glycerol is an alcohol; a fatty acid is RCOOH with a hydrocarbon R group of 4–24 carbons.

Saturated fatty acids

Saturated fatty acids they have no carbon double bonds, form straight chains and are mainly in animal fats.

Unsaturated fatty acids

Unsaturated fatty acids they have double bonds and are mainly in vegetable oils.
- (mono- or polyunsaturated)
Cis fatty acids have H atoms on the same side of the double bond and are metabolised by enzymes.
Trans fatty acids have H atoms on opposite sides, cannot form enzyme–substrate complexes and are linked with coronary heart disease.

Ester bond

Ester bond bond formed by condensation between the hydroxyl of glycerol and the carboxyl of a fatty acid.

One water molecule is released per ester bond, so three water molecules are released per triglyceride.

Part 9 of 12Cholesterol, lipoproteins and reducing risk

Cholesterol
- a lipid made in the body that is needed for membranes, sex hormones and bile, and is transported as lipoproteins.

Type	Contents	Role	Effect
HDL	Unsaturated fat, cholesterol, protein	Carry cholesterol from tissues to the liver to be recycled or excreted	Lower blood cholesterol and help remove it from plaques
LDL	Saturated fat, cholesterol, protein	Carry cholesterol from the liver to the blood and cells via membrane receptors	High levels block receptors so blood cholesterol rises

Cholesterol, lipoproteins and reducing risk

Ratio

Ratio the LDL:HDL ratio matters, with about 3:1 healthy and above 5:1 raising the risk of heart disease.

Evidence linking cholesterol to CVD

Evidence linking cholesterol to CVD high blood cholesterol correlates with CVD.
Statins that lower cholesterol also lower risk, and lowering total cholesterol reduces coronary events.
Plaque regression is seen alongside lipid-lowering therapy.
A third variable, such as alleles affecting fat metabolism, could influence both.

Diet

Diet diets high in saturated fat tend to raise LDL, though some studies are inconclusive.
Food labels and traffic-light labels (red high, orange medium, green low) inform choices on sugar, saturated fat and salt.

Obesity indicators

Obesity indicators waist-to-hip ratio and BMI.
Waist-to-hip ratio should be below 0.86 for women and below 1.0 for men.
BMI mass (kg) ÷ height² (m²);
- below 18.5 is underweight, 18.5–24.9 normal, 25–29.9 overweight and 30 or more obese.

Smoking and exercise

Smoking and exercise research led to packet health warnings, support to stop smoking, more school physical education and campaigns encouraging exercise.

Part 10 of 12Practical: vitamin C content

Principle
- vitamin C (ascorbic acid) is a reducing agent that turns blue DCPIP colourless.

Make six solutions of known vitamin C concentration by serial dilution.

Measure 1 cm³ of DCPIP into a test tube.

Add a vitamin C solution drop by drop from a graduated pipette or burette, shaking for the same time after each drop.

Record the volume needed to turn the DCPIP colourless.

Repeat twice more and calculate a mean, then repeat for each concentration.

Plot volume against concentration with a line of best fit to give a calibration curve.

Repeat with fruit juices and use the curve to estimate their vitamin C concentration.

Result

Result less volume is needed as vitamin C concentration increases.

Safety

DCPIP is an irritant, so avoid skin contact and wear eye protection.

Part 11 of 12More on this topic

Term	Meaning
Dipole	A molecule with an uneven distribution of charge, such as water.
Glycosidic bond	Bond between monosaccharides formed by condensation.
Ester bond	Bond between glycerol and a fatty acid formed by condensation.
Cooperative binding	Shape change after the first oxygen binds that makes further binding easier.
Bohr effect	Reduced haemoglobin affinity for oxygen at high carbon dioxide levels.
Atheroma	Plaque of cholesterol, lipids, macrophages and platelets under the endothelium.
LDL	Lipoprotein that raises blood cholesterol and CVD risk.
Meta-analysis	Analysis combining results from many similar studies.

Part 12 of 12More from the specification

1DCPIP Titration for Vitamin C Quantification

Ascorbic acid acts as a powerful reducing agent that readily donates electrons to decolourise blue DCPIP into a colourless reduced compound.
- (2,6-dichlorophenolindophenol)

2Standard Calibration Curve Construction

Titrating known concentrations of vitamin C against DCPIP produces a calibration graph, enabling determination of vitamin C content in unknown fruit juices from the volume required to decolourise the dye.

3Low-Density Lipoproteins and Cardiovascular Risk

Low-density lipoproteins (LDLs) transport cholesterol from the liver to peripheral tissues;
- excessive circulating LDL accumulates in arterial tunica intima to form atheromatous plaques.

4High-Density Lipoproteins and Endothelial Protection

High-density lipoproteins (HDLs) scavenge excess cholesterol from arterial tissues back to the liver, maintaining vascular lumen patency and preserving oxygen delivery for cellular respiration.

Key terms

Term	Meaning
Risk factor	A factor linked to an increased chance of developing a disease.
Energy budget	Energy input minus energy output.
Glycosidic bond	Covalent bond between two monosaccharides formed by condensation.
Ester bond	Bond between glycerol and a fatty acid formed by condensation.
Triglyceride	A lipid made of glycerol and three fatty acids.
HDL	Lipoprotein that carries cholesterol from tissues to the liver.
LDL	Lipoprotein that carries cholesterol from the liver to cells and blood.
BMI	Body mass in kg divided by height in metres squared.

Avoid these mistakes

Saying a risk factor guarantees disease — it only raises the probability.

Stating that a correlation proves causation — say there is an association unless a mechanism and repeated evidence support it.

Saying glycosidic bonds form by hydrolysis — they form by condensation and are broken by hydrolysis.

Calling LDL always bad and HDL always good — the ratio of LDL to HDL matters.

Last updated: 15 October 2026