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]

2.8.5Inquiry Process

Movement of Joints- Skills — IB Biology HL Revision Notes & Topical Questions

5 min read 5 parts Lesson 90 of 160

📚 IB Biology 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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Part 1 of 5Parts of a Synovial Joint

Cartilage

Cartilage Smooth hyaline cartilage covers the bone ends, reducing friction and absorbing shocks.

Synovial fluid

Synovial fluid A lubricating fluid secreted by the synovial membrane reduces friction and nourishes the cartilage.

Joint capsule

Joint capsule A tough fibrous capsule surrounds the joint and keeps the synovial fluid in place.

Ligaments

Ligaments Strong fibrous bands join bone to bone, stabilising the joint and limiting its range of movement.

Tendons

Tendons Tendons attach muscles to bones so that muscle contraction pulls on the skeleton.

Part 2 of 5Joint Types and Muscle Action

Hinge joint

Hinge joint Found at the elbow and knee, it allows movement in one plane, like a door opening and closing.

Ball and socket joint

Ball and socket joint Found at the hip and shoulder, it allows movement in many directions, including rotation.

Elbow flexion

Elbow flexion The biceps contracts and the triceps relaxes to bend the arm.

Elbow extension

Elbow extension The triceps contracts and the biceps relaxes to straighten the arm.

Joint	Example	Movement
Hinge	Elbow, knee	One plane
Ball and socket	Hip, shoulder	Many planes

Part 3 of 5Levers and Measurement

Levers and Measurement

Lever

Lever The bone acts as a rigid bar, the joint as the pivot, and the muscle supplies the effort force.

Moments

Moments Moment equals force multiplied by perpendicular distance from the pivot;
- balance occurs when moments are equal.

Range of movement

Range of movement A goniometer measures the angle through which a joint can move.

Variables

Variables Compare ages or activities by measuring angle at maximum flexion and extension with repeated trials.

Part 4 of 5Worked Example

Question

The biceps attaches 4 cm from the elbow pivot.
A 5 N weight is held in the hand 30 cm from the pivot.
Ignoring the forearm's weight, calculate the force the biceps must exert to hold the arm still.

Moment of load = 5 N × 0.30 m = 1.5 N m.
Moment of effort = F × 0.04 m.
At balance, F × 0.04 = 1.5.
F = 1.5 ÷ 0.04 = 37.5 N.

Answer The biceps must exert 37.5 N, seven and a half times the weight held.

Part 5 of 5Exam Checklist & Tips

2.8.5 – Key Points for the Exam

Synovial joint A joint with a fluid-filled cavity between bones, allowing free movement.
Ligament Tissue that connects bone to bone.
Tendon Tissue that connects muscle to bone.
Flexor A muscle that bends a joint.
Extensor A muscle that straightens a joint.

Common Mistakes

Mixing up tendons and ligaments.
Saying both antagonistic muscles contract together to move the joint.
Writing that cartilage is bone.
Measuring the lever distance to the bone's end rather than to the pivot.

Last updated: 27 October 2026