Amount of Substance OCR chemistry........

This is a calculation and exam based examples

1. Amount of Substance Content:

2. A chemical formula is a symbolic representation that expresses the composition of a chemical substance using chemical symbols and numbers. This type of formula provides the actual number of each type of atom in a molecule of the compound. The empirical formula represents the simplest, most reduced ratio of different elements in a compound or It gives the lowest whole-number ratio of the elements present in the compound The simplest ratio of atoms of an element in a compound Number of atoms of each element in a molecule

3. Empirical Formulae

4. Mass relative to 1/12 th of Carbon-12 = 1u Formula Unit

5. Steps For Empirical Formula Calculation of Unknown Compounds. Step 1: Work out the molar ratio of the atoms. Step 2: Divide by the smallest number (in this case 0.025) to find the whole number ratio. Step 3: Write the empirical formula.

6. In an experiment, 1.203 g of calcium combines with 2.13 g of chlorine to form a compound [A,: Ca, 40.1; Cl, 35.5].

7. Analysis showed that 0.6175 g magnesium reacted with 3.995 g of bromine to form a compound. Find the empirical formula of this compound. Atomic masses: Mg = 24.3 , Br = 79.9

8. Analysis of a compound showed the following percentage composition by mass: Na = 74.2% , O = 25.8% ( Ar : Na = 23 , O = 16)

9. A empirical formula of CH 2 and a relative molecular mass of 70. What is its molecular formula?

10. Water of crystallization, also known as water of hydration, these are water molecules that are structurally incorporated into the crystal lattice of a chemical compound. This help to maintain shape of crystal in some salts and complex metal oxides.

11. Weigh balance

12. A hydrated carbonate of an unknown Group 1 metal has the formula X 2 CO 3 .10H 2 O and is found to have a relative formula mass of 286. What is the Group 1 metal? Step 1: Work out the relative formula mass of the compound without the metal. Step 2: Work out the atomic mass of the two Group 1 metal atoms.  Step 3: Look on the Periodic Table to find the element.

13. Practical Techniques for Measuring mass or find out Formulae

14. Step 1: Calculate moles of Anhydrous CoCl 2 = C-A= Step 2: Calculate moles of Water: B-C= Step 3: Find the Smallest Whole Number Ratio Step 4: Write down the value of X in CoCl 2 . X H 2 O A B C Mole=   Co= 58.93 CoCl 2 = ?

15. How accurate is an experimental Formula? Assumption 1- All of the water has been lost. Assumption 2- No Further decomposition

16. Mole and Volume

17. Using Volume to measure the amount of substance Liquid and Gases are measured by using the volume. Volume can be converted into the amount of substance. =1ml 1 = 1 litre 1 = = 1000 ml = 1 litre  

18. Converting Volume into Mole: Amount of Substance(n) mol , and Volume of Substance (V) has a link with Concentration (c) mol . n=c × V We usually measure the volume in we need to convert it into by dividing with 1000. So, n = c ×  

19. Solution:

20. Standard Solution A standard solution is a solution of known concentration or composition that is used in analytical chemistry and various laboratory applications as a reference or comparison to determine the concentration or composition of an unknown substance. Volumetric Flask

21. Titration Apparatus

22. How to Calculate the mass of the sample to prepare standard solutions of required molarity?

23. Moles and Gas volume It is difficult to measure the mass of gas but easy to measure the volume of gas. At the same Temperature and pressure, equal Volumes of different gases have the same no. of molecules or particles.

24. Molar Volume The molar gas Volume V m is the volume of gas per mole of gas molecules at standard temperature and pressure. Dependance: Temperature Pressure Note: Max. experiments are performed at RTP .

25. Molar Volume

26. Converting between the amount in moles and volume of gases

27. What do you do when carrying out an experiment where the gases are at different Temperature and Pressure?

28. The assumption for molecules to make up an Ideal gas.

29. Conversion of quantities in the Correct units Pa, K, and before using the ideal gas equation. Normally we do this conversion when an experiment is carrying out  

30. Incorrect Assumption Many people make the incorrect assumption that room temperature is 25 °C (298K), the temperature often regarded as standard temperature for chemistry. Using the ideal gas equation, you can show that the molar gas volume at 25 °C an atmospheric pressure of 101 kPa is actually equal to 24.5  

31. Find Relative molecular mass by Ideal gas equation. Application: You can use the ideal gas equation to find the relative molecular mass of a volatile liquid . Procedure: T he unknown compound would need to be a liquid at room temperature but have a boiling point below 100 °C so that it vaporizes. Add a sample of the volatile liquid to a small syringe via a needle. Weigh the small syringe. Inject the sample into a gas syringe through the self-sealing rubber cap. Reweigh the small syringe to find the mass of the volatile liquid added to the gas syringe. 2. Place the gas syringe in a boiling water bath at 100 °C , 3. The liquid vaporizes and produces a gas and gas pressure is recorded.

32. A 0.320 g sample of a volatile liquid was heated until it vaporized. The resulting vapor then occupied 61.5 cm3 at 101 kPa and 100 °C. Calculate the relative molecular mass of the volatile liquid.

33. The ideal gas equation relies on two key assumptions: Forces between molecules are negligible. Gas molecules have negligible size compared to the size of their container. These assumptions hold at low pressures and high temperatures when the gas molecules are far apart and moving fast.

34. Improvement in Ideal gas equation: Scientists have developed several improvements to the ideal gas equation for real gases. In the real gas equation, corrections have been made to take into account the volume of gas molecules and intermolecular forces.

35. The Van der Waals equation is one of the real gas equations used to describe the behavior of real gases, taking into account the finite volume of gas molecules and the presence of intermolecular forces. It is expressed as: Where: a and b are Van der Waals constants unique to each gas. The Van der Waals equation incorporates two correction terms: a (the "attraction" term) accounts for the attractive forces between gas molecules. It is a measure of how strongly the gas molecules are attracted to each other. b (the "repulsion" term) accounts for the finite volume occupied by gas molecules. It represents the effective volume excluded by the gas molecules themselves.

36. Difference between ideal and real gas Characteristic Ideal Gas Real Gas Particle Volume Negligible (treated as point masses) Significant (finite volume) Intermolecular Forces Negligible (no forces between particles) Present (attractions/repulsions) Behavior at High Pressure Follows ideal gas law Deviates from ideal behavior due to particle volume and interactions Behavior at Low Temperature Follows ideal gas law Deviates from ideal behavior due to reduced kinetic energy and condensation Ideal Gas Law Validity Ideal gas law holds well at low pressures and high temperatures Real gases become more ideal at low temperatures and high pressures

37. Difference Between ideal and Real gas equation Characteristic Ideal Gas Equation Real Gas Equation Formula PV = nRT Various forms (e.g., Van der Waals, Redlich-Kwong) Applicability Ideal gases Real gases Assumptions Negligible particle volume, no intermolecular forces Accounts for particle volume and intermolecular forces Conditions Low pressures, high temperatures High pressures, low temperatures, deviations from ideal behavior Deviations from Ideal Behavior Ideal behavior assumed Describes deviations from ideal behavior

38. Predict the conditions of pressure and temperature that cause the ideal gas equation to break down. Explain your answer. Answer: The ideal gas equation breaks down under high pressure , low temperature , and high gas density conditions because it does not account for the real-world behaviors of gas molecules, including volume exclusion and intermolecular forces . In such cases, more complex equations of state, like the Van der Waals equation are used to describe the behavior of real gases more accurately.

39. Volume Exclusion Volume exclusion, also known as the excluded volume effect , refers to the idea that in a real gas , molecules have finite volumes and cannot occupy the same space simultaneously. This concept is in contrast to the ideal gas assumption, which treats gas particles as point masses with zero volume. Volume exclusion becomes significant at high gas densities and is one of the factors that can cause deviations from ideal gas behavior.

40. 1: Calculate the amount of substance, in moles, in: 50 of a 1.00 mol solution. n = c × 2: Calculate the concentration, in g , for: 2.00 mol of NaOH in 4.00 of solution.