A titration curve plotting pH against volume of titrant added, producing the characteristic S-shaped (sigmoidal) curve used in analytical chemistry. The plot reveals buffer regions, equivalence points, and acid/base strength at a glance. Essential for chemistry education and laboratory analysis, it helps identify when a reaction reaches completion and which indicators are appropriate.
""" anyplot.ai
titration-curve: Acid-Base Titration Curve
Library: pygal 3.1.3 | Python 3.13.14
Quality: 84/100 | Updated: 2026-06-24
"""
import os
import sys
# Prevent the local pygal.py from shadowing the installed pygal package
sys.path = [p for p in sys.path if p and os.path.abspath(p) != os.path.abspath(os.path.dirname(__file__))]
import numpy as np
import pygal
from pygal.style import Style
# Theme tokens
THEME = os.getenv("ANYPLOT_THEME", "light")
PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
INK_MUTED = "#6B6A63" if THEME == "light" else "#A8A79F"
# Imprint palette — semantic positions for this chart
# Series add() order: pH (1) → dpH/dV (2) → equivalence (3) → pH-7 ref (4) → annotation (5)
CHART_PALETTE = (
"#009E73", # pH curve — Imprint brand green (position 1)
"#C475FD", # dpH/dV derivative — Imprint lavender (position 2)
"#AE3030", # equivalence point — matte red (semantic: critical threshold)
INK_MUTED, # pH 7 reference — muted neutral (structural reference)
"#AE3030", # equivalence annotation text (matches line color)
)
# Data — 25 mL of 0.1 M HCl titrated with 0.1 M NaOH
ca, va = 0.1, 25.0
cb = 0.1
equivalence_vol = va * ca / cb # 25.0 mL
volume_ml = np.linspace(0.01, 50.0, 500)
ph = np.empty_like(volume_ml)
for i, v in enumerate(volume_ml):
moles_h = ca * va - cb * v
total_vol = va + v
if moles_h > 1e-10:
ph[i] = -np.log10(moles_h / total_vol)
elif moles_h < -1e-10:
oh_conc = -moles_h / total_vol
ph[i] = 14.0 + np.log10(oh_conc)
else:
ph[i] = 7.0
# Derivative dpH/dV — normalised 0-1 so the right axis has clean labels
dpH_dV = np.gradient(ph, volume_ml)
dpH_dV = np.clip(dpH_dV, 0, None)
dpH_dV = dpH_dV / dpH_dV.max() # peak = 1.0
eq_vol = equivalence_vol
eq_ph = 7.0
# Title — 45 chars < 67 baseline → full title_font_size=66
title_str = "titration-curve · python · pygal · anyplot.ai"
# Style — Imprint palette, theme-adaptive chrome
custom_style = Style(
background=PAGE_BG,
plot_background=PAGE_BG,
foreground=INK,
foreground_strong=INK,
foreground_subtle=INK_MUTED,
colors=CHART_PALETTE,
title_font_size=66,
label_font_size=56,
major_label_font_size=44,
legend_font_size=44,
value_font_size=36,
stroke_width=2.5,
font_family="'Helvetica Neue', 'Helvetica', 'Arial', sans-serif",
)
# Subsample — 100 points gives a smooth curve with fast render
step = 5
curve_pts = [(float(volume_ml[i]), float(ph[i])) for i in range(0, len(volume_ml), step)]
deriv_pts = [(float(volume_ml[i]), float(dpH_dV[i])) for i in range(0, len(volume_ml), step)]
eq_line_pts = [(float(eq_vol), 0.0), (float(eq_vol), 14.0)]
ref_ph7_pts = [(0.0, 7.0), (50.0, 7.0)]
# Chart — single XY with secondary y-axis for dpH/dV overlay
chart = pygal.XY(
style=custom_style,
width=3200,
height=1800,
title=title_str,
x_title="Volume of NaOH added (mL)",
y_title="pH",
secondary_range=(0.0, 0.7),
show_dots=False,
show_x_guides=False,
show_y_guides=True,
range=(0.0, 14.0),
xrange=(0.0, 50.0),
legend_at_bottom=True,
legend_at_bottom_columns=2,
legend_box_size=30,
truncate_legend=-1,
margin=30,
margin_top=100,
margin_left=180,
margin_right=200,
margin_bottom=160,
tooltip_fancy_mode=True,
x_value_formatter=lambda x: f"{x:.1f}",
y_value_formatter=lambda y: f"{y:.1f}",
)
# Series — color order follows CHART_PALETTE positions
chart.add(
"pH (0.1 M HCl + NaOH)",
curve_pts,
show_dots=False,
stroke_style={"width": 8, "linecap": "round", "linejoin": "round"},
)
chart.add(
"dpH/dV (normalised, right axis)",
deriv_pts,
secondary=True,
show_dots=False,
stroke_style={"width": 6, "linecap": "round", "linejoin": "round"},
)
chart.add(
f"Equivalence ({eq_vol:.0f} mL, pH {eq_ph:.0f})",
eq_line_pts,
show_dots=False,
stroke_style={"width": 3, "dasharray": "14,8"},
)
chart.add("pH 7 Reference", ref_ph7_pts, show_dots=False, stroke_style={"width": 2, "dasharray": "6,6"})
# Direct text annotation at equivalence point — positioned to the right of the vertical line
ann_label = f"{eq_vol:.0f} mL, pH {eq_ph:.0f}"
chart.add(
f"Eq. point: {ann_label}",
[(float(eq_vol + 2.5), float(eq_ph + 2.0))],
show_dots=True,
dots_size=10,
print_values=True,
value_formatter=lambda _: ann_label,
stroke=False,
)
# Save
chart.render_to_png(f"plot-{THEME}.png")
with open(f"plot-{THEME}.html", "wb") as f:
f.write(chart.render())
Part of Acid-Base Titration Curve on anyplot.ai.