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KS3 Science Quizzes

GCSE KS4 Science-Chemistry

Advanced Level Chemistry

docb4_73calcs11msc updated Jan 17th 2008
KS4 SCIENCE - Additional & Applied Chemistry help AQA GCSE Science - Chemistry CCEA GCSE Science - Chemistry Edexcel GCSE 360Science - Chemistry OCR GCSE 21st Century Science Suite - Chemistry  OCR GCSE Gateway Science Suite - Chemistry OCR GCSE Applied Science - Chemistry (double award) WJEC GCSE Science - Chemistry

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On-line Chemistry CALCULATIONS for KS4 Science - GCSE and AS(basic) Chemistry courses.

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study examples carefully11. Molarity and the concentration of solutionsstudy examples carefully

volumetric apparatus

  • Revise section 7. moles and mass before proceeding in this section 11 and eventually you may need to be familiar with the use of the apparatus illustrated above, some of which gives great accuracy when dealing with solutions and some do not.

  • It is very useful to be know exactly how much of a dissolved substance is present in a solution of particular concentration or volume of a solution. So we need a standard way of comparing the concentrations of solutions. 
  • The concentration of an aqueous solution is usually expressed in terms of moles of dissolved substance per cubic decimetre, mol dm-3, this is called molarity, sometimes denoted in shorthand as M.
    • Note: 1dm3 = 1 litre = 1000ml = 1000 cm3, so dividing cm3/1000 gives dm3, which is handy to know since most volumetric laboratory apparatus is calibrated in cm3 (or ml), but solution concentrations are usually quoted in molarity, that is mol/dm3 (mol/litre).
  • Equal volumes of solution of the same molar concentration contain the same number of moles of solute i.e. the same number of particles as given by the chemical formula.
  • You need to be able to calculate
    • the number of moles or mass of substance in an aqueous solution of given volume and concentration
    • the concentration of an aqueous solution given the amount of substance and volume of water, for this you use the equation ....
    • (1a) molarity (concentration) of Z = moles of Z / volume in dm3
      • you need to be able to rearrange this equation ...
      • therefore (1b)  moles = molarity (concentration) x volume in dm3
      • and (1c) volume in dm3 = moles / molarity (concentration)
    • You may also need to know that ...
      • (2) molarity x formula mass of solute = solute concentration in g/dm3,
        • and dividing this by 1000 gives the concentration in g/cm3, and
      • (3) (concentration in g/dm3) / formula mass = molarity in mol/dm3,
        • both equations (2) and (3) result from equations (1) and (4), work it out for yourself.
    • and don't forget by now you should know:
      • (4) moles Z = mass Z / formula mass of Z
      • and (5) 1 mole = formula mass in grams

  • Example 11.1

    • What mass of sodium hydroxide (NaOH) is needed to make up 500 cm3 (0.5 dm3) of a 0.5M solution? [Ar's: Na = 23, O = 16, H = 1]

    • 1 mole of NaOH = 23 + 16 + 1 = 40g

    • for 1000 cm3 (1 dm3) of 0.5M you would need 0.5 moles NaOH

    • which is 0.5 x 40 = 20g

    • however only 500 cm3 of solution is needed compared to 1000 cm3

    • so scaling down: mass NaOH required = 20 x 500/1000 = 10g

  • Example 11.2

    • How many moles of H2SO4 are there in 250cm3 of a 0.8M sulphuric acid solution? What mass of acid is in this solution? [Ar's: H = 1, S = 32, O = 16]

    • formula mass of sulphuric acid = 2 + 32 + (4x16) = 98, so 1 mole = 98g

    • if there was 1000 cm3 of the solution, there would be 0.8 moles H2SO4

    • but there is only 250cm3 of solution, so scaling down ...

    • moles H2SO4 = 0.8 x (250/1000) = 0.2 mol

    • mass = moles x formula mass, which is 0.2 x 98 = 19.6g of H2SO4 

  • Example 11.3

    • 5.95g of potassium bromide was dissolved in 400cm3 of water. Calculate its molarity. [Ar's: K = 39, Br = 80]

    • moles = mass / formula mass, (KBr = 39 + 80 = 119)

    • mol KBr = 5.95/119 = 0.05 mol

    • 400 cm3 = 400/1000 = 0.4 dm3

    • molarity = moles of solute / volume of solution

    • molarity of KBr solution = 0.05/0.4 = 0.125M

  • Example 11.4

    • What is the concentration of sodium chloride (NaCl) in g/dm3 and g/cm3 in a 1.50 molar solution?

    • At. masses: Na = 23, Cl = 35.5, formula mass NaCl = 23 + 35.5 = 58.5

    • Therefore concentration = 1.5 x 58.5 = 87.8 g/dm3, and

    • concentration = 87.75 / 1000 = 0.0878 g/cm3

  • Example 11.5

    • A solution of calcium sulphate (CaSO4) contained 0.5g dissolved in 2dm3 of water. Calculate the concentration in (a) g/dm3, (b) g/cm3 and (c) mol/dm3.

    • (a) concentration = 0.5/2 = 0.25 g/dm3, then since 1dm3 = 1000 cm3

    • (b) concentration = 0.25/1000 = 0.00025 g/cm3

    • (c) At. masses: Ca = 40, S = 32, O = 64, f. mass CaSO4 = 40 + 32 + (4 x 16) = 136

      • moles CaSO4 = 0.5 / 136 = 0.00368 mol

      • concentration CaSO4 = 0.00368 / 2 = 0.00184 mol/dm3

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    These chemical calculations pages of revision notes will also prove useful for basic revision for students studying revising tutoring teaching Advanced Level GCE AS A2 IB CHEMISTRY courses in unofficial support the Chemistry in any advanced-subsidiary AQA, EDEXCEL, OCR, CIE, WJEC, SQA and CCEA (NI) UK or Cambridge/London/Edexcel International and OCR/CIE International examinations.

    KS4 SCIENCE - Additional & Applied Chemistry help AQA GCSE Science - Chemistry CCEA GCSE Science - Chemistry Edexcel GCSE 360Science - Chemistry OCR GCSE 21st Century Science Suite - Chemistry  OCR GCSE Gateway Science Suite - Chemistry OCR GCSE Applied Science - Chemistry (double award) WJEC GCSE Science - Chemistry

    ks4 science examinations gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision * SITE PURPOSE EDUCATION - online learning or 'self-private-tuition' using revision notes, quizzes, practice tests involving GCSE Science CHEMISTRY in the areas of REVISING only the CHEMISTRY-Earth Science-Radioactivity at Doc Brown's Chemistry Clinic via HOMEPAGE in secondary school/schools, 6th form college/colleges, academy/academies or home self-study. Hopefully it will encourage interest and understanding of Chemistry, Earth Science and Radioactivity in any country of the world, though the site is written entirely in English. The website is designed to help and unofficially support students/teachers revise-learn/teach the chemistry for modular or co-ordinated examination science courses from UK QCA based AQA, OCR (Oxford and Cambridge) Twenty First (21st) Century and Gateway Science, Edexcel 360Science , Nuffield, Salters, Cambridge International (CIE), London International, WJEC, CCEA exams etc. Also, national award assessments-examinations for GCSE-IGCSE-KS4-O level-BTEC-NVQ applied, additional and chemistry national science courses. Also covers, mainly via quizzes the UK National KS3 SATs Science-biology/chemistry/physics (SAT revision levels 3-5 or 5-7) and covers much of the revising, learning and teaching chemistry examinations for the national curriculum for secondary schools and colleges. The site does not support the content of England, Wales or Northern Ireland primary science KS1 or KS2. The notes should also provide some background theory for a coursework assignment or project. BUT please note that my on-line revision notes and quizzes are no substitute for good classroom teaching-lecturing and thorough studying of your own notes and textbooks, practicing past papers and a copy of the syllabus which are readily downloaded from the examination board sites, but I hope here and there they will lend a tutoring hand on some topic, unit, module etc. For final revision you have to be intellectually honest about what you don't know or follow, YOU have to take the stuff to pieces, analyse what you do/do not understand and reconstruct it so it all makes sense in the end. There is no other way, there are no magic secrets on how to revise and learn, its mainly down to hard work and just good old fashioned study and employing teach-yourself strategies without the need for extra tutors and tutoring lessons. I also think there is too much hit and miss revision using past papers (which I do NOT supply) and not enough systematic revision. I also hope it will help teachers in planning lessons and developing schemes of work for science-chemistry. There are no lesson plans on the site but there are plenty of quizzes to incorporate into classroom activities whether photocopied or on electronic whiteboard projector for use as self-tuition-assessment purposes and a variety of teaching and learning styles and the images may be used in Microsoft Word documents and powerpoint projections. The site seems to be used by a large number of home study tutors, particularly the revision notes. An individual tutor may print out the notes for science-chemistry learning teaching-tuition purposes and for background material for assignments and projects. I have no interest or time in producing WORD.doc or xxxx.pdf files of the notes at the moment. Neither have I time to write up many practical laboratory experiments ('lab'-'labs') at the moment, but the notes contain lots of background information of chemical reactions in terms of observations-balanced equations-reactants-products-theory etc. I also find it difficult to recommend specific exam websites or syllabus textbooks, it depends exactly on what you need, what you have time for, and there are so many of them to choose from and I do not supply past examination papers for classes. The sites resources include revision notes, quizzes and worksheets which provide support for home study or tuition for homework and coursework help e.g. science investigations for any of the key stage courses indicated, but I do not supply lesson plans.  Dr W P Brown gcse 10-11-2007 *  ks4 science examinations gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision

    KS3 Science Quizzes

    GCSE KS4 Science-Chemistry

    Advanced Level Chemistry

    docb4_73calcs11msc updated Jan 17th 2008

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