\[\boxed{10}.\]1. A science educator is organizing a hands-on chemistry activity involving titration. She needs 0.5 liters of 0.2 M hydrochloric acid for each of 8 student groups. If she has a 2-liter stock solution of 1.0 M HCl, how many liters of water must she add to dilute the stock solution sufficiently for all groups?

["Title: Mastering Titration: How Much Water to Dilute 2L of 1.0 M HCl for Student Lab Activities", "When preparing for hands-on chemistry labs—especially titration experiments—precision is essential. A common challenge for science educators is accurately diluting concentrated acid solutions to meet precise experimental requirements. This article breaks down a real-world dilution problem faced by a chemistry teacher organizing student titration activities, showing exactly how much water to add to a 2-liter stock of 1.0 M HCl to produce enough 0.2 M solution for eight student groups.", "---", "### The Challenge", "Each of 8 student groups needs 0.5 liters of 0.2 M hydrochloric acid (HCl) for a titration experiment. First, calculate the total volume of diluted solution needed:", "[\n\ ext{Total volume} = 8 \ imes 0.5,\ ext{L} = 4,\ ext{L}\n]", "The target concentration is 0.2 M, and the stock solution is 1.0 M. Use the dilution formula:", "[\nC_1 V_1 = C_2 V_2\n]", "Where:\n- ( C_1 = 1.0,\ ext{M} ) (stock concentration)\n- ( V_1 = ? ) (volume of stock needed)\n- ( C_2 = 0.2,\ ext{M} ) (desired concentration)\n- ( V_2 = 4,\ ext{L} ) (final diluted volume)", "Solve for ( V_1 ):", "[\n1.0 \ imes V_1 = 0.2 \ imes 4\n]\n[\nV_1 = \frac{0.8}{1.0} = 0.8,\ ext{L}\n]", "This means only 0.8 liters of the 1.0 M HCl stock is required to make 4 liters of 0.2 M solution. The remaining volume must be water.", "---", "### Calculating Water to Add", "Total volume needed: 4 L\nVolume of concentrated acid: 0.8 L\nVolume of water to add:", "[\n4,\ ext{L} - 0.8,\ ext{L} = 3.2,\ ext{L}\n]", "---", "### Final Details", "- Stock solution volume: 0.8 L (1.0 M HCl)\n- Water to add: 3.2 liters\n- Final volume: 4.0 L of 0.2 M HCl\n- Number of groups: 8", "This precise dilution ensures safe, accurate titration experiments while minimizing waste and cost. For educators running chemistry labs, mastering such calculations guarantees consistent results and student safety—key outputs of effective science teaching.", "---", "### Why This Matters in Titration", "Titration accuracy depends on a precisely controlled acid or base concentration. Diluting concentrated HCl properly prevents under- or over-use of reagents, which could skew results or pose safety risks. With this method, educators prepare exactly the right amount of solution—no more, no less—supporting reliable student learning.", "---", "Summary:\nTo prepare 4.0 L of 0.2 M HCl from a 1.0 M stock, dilute 0.8 L of stock with 3.2 liters of water. Perfect for classroom titration labs and student success.", "---", "Keywords: titration lab, HCl dilution, chemistry teaching tips, diluted HCl recipe, accurate acid concentration, 1.0 M to 0.2 M dilution, student science experiments, laboratory preparation"]