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]

Tools and Inquiry — IB Physics skills

Tools and Inquiry — IB Physics skills — IB Physics HL Revision Notes & Topical Questions

5 min read 12 parts Lesson 1 of 22 Unit quiz

📚 IB Physics HL 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

Tools and Inquiry — IB Physics skills — IB PHYSICS HL notes: Apply safety, ethical and environmental considerations, choose measuring instruments, and use SI units, vectors and scale diagrams in IB Physics.Risk assessment — identify the hazards, judge the level of risk and change…

General laboratory
Specific precautions
Electricity use
Identified concern
Liquid-in-glass thermometer
Digital temperature probe

Part 1 of 9Hazards in physics experiments

Situation	Hazard	Precaution
Radioactive sources	Ionising radiation	Lead-lined labelled storage, shortest possible use, tongs, never point at anyone, trained teacher, safe distance
Electron diffraction	High voltage	Only qualified staff set up, apparatus earthed and checked, no touching live connections
Lasers	Eye damage	Never direct at people or reflective surfaces, keep the beam horizontal below eye level, goggles if available, switch off when done
Electric circuits	Shock and short circuits	Low voltages (1.5 V cells, up to 9 V), mains equipment earthed and inspected, no bare wires, away from water
Hot water and gas experiments	Burns, scalds and breakage	Keep apparatus away from table edges, never leave unattended, gloves when sealing bungs, shield glass tubes under pressure
Boyle's law apparatus	Pressure and explosion	Do not overfill syringes or pumps and shield glass tubes

Part 2 of 9Ethical and environmental issues

Ethics

Ethics physics rarely raises ethical issues, but human subjects need consent and animal work must follow experimentation protocols
If none is found, say so and justify it

Electricity use

Electricity use mains power has an environmental cost from fossil fuels
Switch off equipment, use low-voltage supplies and efficient devices

Water use

Water use reuse the same water across trials and dispose of contaminated water following laboratory guidelines

Batteries

Batteries improper disposal causes fire risk and toxic release
Recycle them or use rechargeable cells or mains equipment

Waste

Waste reuse or recycle materials and dispose of them properly

Identified concern

Identified concern explain how the impact will be reduced

Part 3 of 9Measuring mass, time, length, volume and force

Mass

Mass digital balance usually to two decimal places
Tare (zero) it before use and record in kilograms

Time

Time stopwatch or stop-clock
Human reaction time matters for intervals under about a second, so use light gates or a data logger
1 minute = 60 seconds

Length

Length a ruler to the nearest millimetre, a tape measure for larger distances and a micrometer for small ones
The standard unit is the metre

Volume

Volume measuring cylinder, and the change in volume gives the volume of an irregular solid
1 ml of water = 1 cm³

Force

Force force meter or spring balance

Part 4 of 9Measuring temperature, electrical quantities, angle, sound and light

Measuring temperature, electrical quantities, angle, sound and light

Liquid-in-glass thermometer

Liquid-in-glass thermometer reads to 1 °C or 0.5 °C and is simple, robust and cheap but slow to equilibrate and less precise

Digital temperature probe

Digital temperature probe thermistor or thermocouple reading to ±0.1 °C
It responds quickly and suits data logging

Ammeter

Ammeter connected in series and measures charge per unit time

Voltmeter

Voltmeter connected in parallel across the component

Analogue meters

Analogue meters check for zero error and subtract it, and avoid parallax error by reading perpendicular to the scale

Digital meters

Digital meters read very small values in mA, μA, mV or μV, are easy to use and may flicker between values

Angle

Angle use a protractor with precision ±0.5°, align the baseline carefully and read at eye level
Measure from a drawn normal line to the centre of the ray

Sound intensity

Sound intensity sound level meter to about ±0.1 dB
Hold it at a fixed distance and avoid background noise

Light intensity

Light intensity light meter, photodiode or lux meter
Keep the detector perpendicular to the source and shield from stray light

Part 5 of 9SI units and prefixes

Base units

Base units length (metre, m), mass (kilogram, kg), time (second, s), electric current (ampere, A), temperature (kelvin, K), amount of substance (mole, mol) and luminous intensity
- (candela, cd; not used in IB Physics)

Derived units

Derived units they come from definitions, such as N = kg m s⁻², J = kg m² s⁻² and Pa = kg m⁻¹ s⁻²

Prefixes

Prefixes powers of ten such as kW (× 10³ W), cm (× 10⁻² m) and mg (× 10⁻³ g)
The list is in the data booklet

Symbols

Symbols the same symbol can mean different quantities, such as c for the speed of light or specific heat capacity

Part 6 of 9Scalars and vectors

1Scalar

Scalar a quantity with magnitude only, such as distance, speed, mass, time, energy, density, pressure and temperature

2Vector

Vector a quantity with magnitude and direction, such as displacement, velocity, acceleration, force and momentum

3Distance and displacement

Distance and displacement distance is the total path length and displacement is the straight-line length and direction from start to finish

4Speed and velocity

Speed and velocity an object can have constant speed but changing velocity if its direction changes

5Representation

Representation an arrow whose head gives the direction and whose length gives the magnitude

6Test

Test two 5 N forces give a total between 0 N and 10 N, so force is a vector, while two 5 kg masses always give 10 kg

7Negative values

Negative values work and energy can be negative but are scalars

8Product

Product a scalar times a vector is a vector, as in F = ma and p = mv

Part 7 of 9Combining and resolving vectors

Triangle method

Triangle method place the vectors head to tail and the resultant joins the start to the end

Parallelogram method

Parallelogram method place the vectors tail to tail

Subtraction

Subtraction c = a − b is a + (−b)

Perpendicular vectors

Perpendicular vectors the magnitude comes from Pythagoras and the angle from tan θ

Resolving

Resolving a vector F at angle θ to the horizontal has F_x = F cos θ and F_y = F sin θ

Hiker

6 km east and 10 km north gives a displacement of 11.7 km at 59° above the horizontal

Cosine

Cosine it always goes with the adjacent side

Part 8 of 9Scale diagrams and approximations

When

When use calculation for perpendicular vectors and scale drawing when they are not at right angles

Method

Method choose a scale such as 1 cm = 1 km so the drawing is large, use a sharp pencil, ruler and protractor, draw the vectors head to tail accurate to 1 mm,
then draw the resultant from start to finish

Reading

Reading measure its length and convert with the scale and measure the angle with a protractor
- (5 cm at 1 cm = 2 km is 10 km)

Negligible quantities

Negligible quantities ignore effects much smaller than the others,
- such as heat lost to the surroundings, the internal resistance of a supply small compared with the load or the mass of a pendulum string compared with the bob

Part 9 of 9More from the specification

Variable

A factor that can change in an investigation.

Potential difference

Work done by a unit charge passing through a component.

Key terms

Term	Meaning
Risk assessment	Identifying hazards, judging the risk and altering the procedure to reduce it.
SI base unit	One of the seven fundamental units from which all other units are derived.
Scalar	A quantity with magnitude only.
Vector	A quantity with both magnitude and direction.
Resultant	The single vector with the same effect as two or more vectors.
Component	One of the perpendicular parts into which a vector is resolved.
Negligible	Small enough that its effect can be ignored in a model.
Zero error	A reading on an instrument when the true value is zero, which must be subtracted.

Avoid these mistakes

Writing generic safety statements — state a specific precaution linked to the hazard.

Forgetting to tare a balance or to convert quantities to SI units.

Treating human reaction time as negligible for very short time intervals.

Adding vectors as if they were scalars, or using Pythagoras when the vectors are not at right angles.

Claiming there are no ethical issues without justifying the statement.

Last updated: 13 October 2026